Document:

<PAGE>
                                                                    EXHIBIT 10.8

                           THIRD AMENDED AND RESTATED
                            INVESTOR RIGHTS AGREEMENT

         THIS THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT (the
"AGREEMENT") is entered into as of the 21st day of August, 2001, by and among
MYOGEN, INC., a Delaware corporation (the "COMPANY"), CERTAIN HOLDERS OF COMMON
STOCK of the Company set forth on Exhibit A hereto (each, a "COMMON
STOCKHOLDER"), PURCHASERS OF THE COMPANY'S SERIES A PREFERRED STOCK ("SERIES A
STOCK") set forth on Exhibit B hereto, PURCHASERS OF THE COMPANY'S SERIES C
PREFERRED STOCK (the "SERIES C STOCK") set forth on Exhibit B hereto and
PURCHASERS OF THE COMPANY'S SERIES D PREFERRED STOCK (the "SERIES D STOCK") set
forth on Exhibit B hereto. The purchasers of the Series A Stock, Series C Stock
and Series D Stock shall be referred to hereinafter as the "INVESTORS" and each
individually as an "INVESTOR."

                                    RECITALS

         WHEREAS, the Company has granted registration rights, information
rights and certain other rights pursuant to that certain Second Amended and
Restated Investor Rights Agreement dated November 23, 1999 (the "PRIOR
AGREEMENT");

         WHEREAS, the Company proposes to sell and issue the Shares of Series D
Stock as defined in that certain Series D Preferred Stock Purchase Agreement
dated August 21, 2001 (the "PURCHASE AGREEMENT"); and

         WHEREAS, as a condition of entering into the Purchase Agreement, the
Investors have requested that the Company extend to them registration rights,
information rights and other rights as set forth below, and the Company and the
parties to the Prior Agreement are willing to amend the rights given to them
pursuant to the Prior Agreement by replacing such rights in their entirety with
the rights set forth in this Agreement.

         NOW, THEREFORE, in consideration of the mutual promises,
representations, warranties, covenants and conditions set forth in this
Agreement and in the Purchase Agreement, the parties mutually agree as follows:

SECTION 1. GENERAL

         1.1 AMENDMENT AND RESTATEMENT OF PRIOR AGREEMENT; WAIVER. All of the
undersigned parties who were parties to the Prior Agreement and who constitute
the requisite parties to amend the Prior Agreement hereby (i) waive any right of
first refusal, preemptive right, or other right to purchase any shares of Series
D Preferred Stock being sold pursuant to the Purchase Agreement, on behalf of
themselves and all others, and (ii) agree that the Prior Agreement is null and
void and superseded in all respects by this Agreement.

                                       1
<PAGE>

         1.2 CERTAIN DEFINITIONS. As used in this Agreement the following terms
shall have the following respective meanings:

                  "CO-SALE STOCK" means shares of the Company's Common Stock or
Preferred Stock now legally or beneficially owned or subsequently legally or
beneficially acquired by the Common Stockholders. "Beneficial" ownership shall
have the meaning as set forth in Rule 13-d promulgated under the Exchange Act.
The number of Equity Securities owned by each Common Stockholder is set forth on
Exhibit A, which exhibit shall be amended from time to time to reflect changes
in the number of Equity Securities owned by the Common Stockholders.

                  "COMMON STOCK" means the Company's Common Stock.

                  "EQUITY SECURITIES" means (i) any Common Stock, Preferred
Stock or other security of the Company, (ii) any security convertible, with or
without consideration, into any Common Stock, Preferred Stock or other security
(including any option to purchase such a convertible security), (iii) any
security carrying any warrant or right to subscribe to or purchase any Common
Stock, Preferred Stock or other security or (iv) any such warrant or right.

                  "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended.

                  "FORM S-3" means such form under the Securities Act as in
effect on the date hereof or any successor registration form under the
Securities Act subsequently adopted by the SEC which permits inclusion or
incorporation of substantial information by reference to other documents filed
by the Company with the SEC.

                  "HOLDER" means any Investor who holds Registrable Securities
and any holder of Registrable Securities to whom the registration rights
conferred by this Agreement have been transferred in compliance with Section
2.10 hereof.

                  "INITIAL OFFERING" means the Company's first firm commitment
underwritten public offering of its Common Stock registered under the Securities
Act.

                  "ORIGINAL ISSUE PRICE" means US $1.375.

                  "PREFERRED STOCK" means any series of the Company's Preferred
Stock.

                  "QUALIFIED PUBLIC OFFERING" means the closing of a firmly
underwritten public offering pursuant to an effective registration statement
under the Securities Act covering the offer and sale of Common Stock for the
account of the Company in which in which (i) the per share price is at least two
(2) times the Original Issue Price (as adjusted for stock splits, dividends,
recapitalizations and the like) and (ii) the cash proceeds to the Company (after
underwriting discounts, commissions and fees) are at least $25,000,000.

                  "REGISTER," "REGISTERED," and "REGISTRATION" refer to a
registration effected by preparing and filing a registration statement in
compliance with the Securities Act and applicable rules and regulations
thereunder, and the declaration or ordering of the effectiveness of such
registration statement.

                                       2
<PAGE>

                  "REGISTRABLE SECURITIES" means (i) Common Stock of the Company
issued or issuable upon conversion of the Shares; and (ii) any Common Stock of
the Company issued as (or issuable upon the conversion or exercise of any
warrant, right or other security which is issued as) a dividend or other
distribution with respect to, or in exchange for or in replacement of, such
above-described securities. Notwithstanding the foregoing, Registrable
Securities shall not include any securities sold by a person to the public
either pursuant to a registration statement or Rule 144 or sold in a private
transaction in which the transferor's rights under Section 2 of this Agreement
are not assigned.

                  "REGISTRABLE SECURITIES THEN OUTSTANDING" shall be the number
of shares determined by calculating the total number of shares of the Company's
Common Stock that are Registrable Securities and either (1) are then issued and
outstanding or (2) are issuable pursuant to then exercisable or convertible
securities.

                  "REGISTRATION EXPENSES" shall mean all expenses incurred by
the Company in complying with Sections 2.2, 2.3 and 2.4, hereof, including,
without limitation, all registration and filing fees (exclusive of underwriting
discounts and commissions), printing expenses, fees and disbursements of counsel
for the Company, reasonable fees and disbursements of a single special counsel
for the Holders, blue sky fees and expenses and the expense of any special
audits incident to or required by any such registration (but excluding the
compensation of regular employees of the Company which shall be paid in any
event by the Company).

                  "SECURITIES ACT" shall mean the Securities Act of 1933, as
amended.

                  "SELLING EXPENSES" shall mean all underwriting discounts,
selling commissions and stock transfer taxes applicable to the sale of
Registrable Securities and fees and disbursements of counsel for any Holder
(other than the fees and disbursements of counsel included in the Registration
Expenses).

                  "SHARES" shall mean shares of the Company's Series A Preferred
Stock, Series C Preferred Stock and Series D Preferred Stock.

                  "SEC" or "COMMISSION" means the Securities and Exchange
Commission or any other federal agency at the time administering the Securities
Act.

SECTION 2. REGISTRATION; RESTRICTIONS ON TRANSFER

         2.1 RESTRICTIONS ON TRANSFER.

                  (a) Each Holder agrees not to make any disposition of all or
any portion of the Shares or Registrable Securities unless and until:

                           (i) There is then in effect a registration statement
under the Securities Act covering such proposed disposition and such disposition
is made in accordance with such registration statement; or

                           (ii) (A) The transferee has agreed in writing to be
bound by the terms of this Agreement, (B) such Holder shall have notified the
Company of the proposed disposition

                                       3
<PAGE>

and shall have furnished the Company with a detailed statement of the
circumstances surrounding the proposed disposition, and (C) if reasonably
requested by the Company, such Holder shall have furnished the Company with an
opinion of counsel, reasonably satisfactory to the Company, that such
disposition will not require registration of such shares under the Securities
Act. It is agreed that the Company will not require opinions of counsel for
transactions made pursuant to Rule 144 except in unusual circumstances.

                           (iii) Notwithstanding the provisions of paragraphs
(i) and (ii) above, no such registration statement or opinion of counsel shall
be necessary for a transfer (A) by a Holder which is a partnership to its
partners or retired partners in accordance with partnership interests, (B) by a
Holder which is a limited liability company to its members or former members in
accordance with their interest in the limited liability company, (C) by a Holder
to the Holder's family member, estate, trust or other entity for the benefit of
an individual Holder or such Holder's family member or (D) by a Holder to such
Holder's affiliate, provided the transferee will be subject to the terms of this
Agreement to the same extent as if he, she or it were an original Holder
hereunder.

                  (b) Each certificate representing Shares or Registrable
Securities shall (unless otherwise permitted by the provisions of the Agreement)
be stamped or otherwise imprinted with a legend substantially similar to the
following (in addition to any legend required under applicable state securities
laws or as provided elsewhere in this Agreement):

                  THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED
                  UNDER THE SECURITIES ACT OF 1933 (THE "ACT") AND MAY NOT BE
                  OFFERED, SOLD OR OTHERWISE TRANSFERRED, ASSIGNED, PLEDGED OR
                  HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER THE ACT OR
                  UNLESS THE COMPANY HAS RECEIVED AN OPINION OF COUNSEL OR OTHER
                  EVIDENCE, SATISFACTORY TO THE COMPANY AND ITS COUNSEL THAT
                  SUCH REGISTRATION IS NOT REQUIRED.

                  (c) The Company shall be obligated to reissue promptly
unlegended certificates at the request of any holder thereof if the holder shall
have obtained an opinion of counsel (which counsel may be counsel to the
Company) reasonably acceptable to the Company to the effect that the securities
proposed to be disposed of may lawfully be so disposed of without registration,
qualification or legend.

                  (d) Any legend endorsed on an instrument pursuant to
applicable state securities laws and the stop-transfer instructions with respect
to such securities shall be removed upon receipt by the Company of an order of
the appropriate blue sky authority authorizing such removal.

         2.2 DEMAND REGISTRATION.

                  (a) Subject to the conditions of this Section 2.2, if the
Company shall receive a written request from the Holders of more than thirty
percent (30%) (as adjusted for stock dividends, stock splits and combinations)
of the Registrable Securities (the "INITIATING HOLDERS")

                                       4
<PAGE>

that the Company file a registration statement under the Securities Act covering
the registration of Registrable Securities having an anticipated aggregate
offering price to the public of at least $5,000,000 (a "PUBLIC OFFERING"), then
the Company shall, within twenty (20) days of the receipt thereof, give written
notice of such request to all Holders, and subject to the limitations of this
Section 2.2, use its best efforts to effect, as soon as practicable, the
registration under the Securities Act of all Registrable Securities that the
Holders request to be registered, including any Registrable Securities of any
Holder joining in such request as are specified in a notice given by any such
Holder to the Company within twenty (20) days after receipt of the Company's
notice.

                  (b) If the Initiating Holders intend to distribute the
Registrable Securities covered by their request by means of an underwriting,
they shall so advise the Company as a part of their request made pursuant to
this Section 2.2 and the Company shall include such information in the written
notice referred to in Section 2.2(a). In such event, the right of any Holder to
include its Registrable Securities in such registration shall be conditioned
upon such Holder's participation in such underwriting and the inclusion of such
Holder's Registrable Securities in the underwriting unless otherwise mutually
agreed by a majority in interest of the Initiating Holders and such Holder to
the extent provided herein. All Holders proposing to distribute their securities
through such underwriting shall (together with the company as provided in
Section 2.6(e)) enter into an underwriting agreement in customary form with the
underwriter or underwriters selected for such underwriting by a majority in
interest of the Initiating Holders (which underwriter or underwriters shall be
reasonably acceptable to the Company). Notwithstanding any other provision of
this Section 2.2 if the underwriter advises the Company that marketing factors
require a limitation of the number of securities to be underwritten (including
Registrable Securities) then the Company shall so advise all Holders of
Registrable Securities which would otherwise be underwritten pursuant hereto,
and the number of shares that may be included in the underwriting shall be
allocated to the Holders of such Registrable Securities on a pro rata basis
based on the number of Registrable Securities held by all such Holders
(including the Initiating Holders); provided that, in no event shall the number
of shares to be included in such underwriting be reduced to less than 30% of the
number of Registrable Securities subject to the request provided in this Section
2.2(b). Any Registrable Securities excluded or withdrawn from such underwriting
shall be withdrawn from the registration.

                                       5
<PAGE>

                  (c) The Company shall not be required to effect a registration
pursuant to this Section 2.2 prior to the earlier of (i) the third anniversary
of the date of this Agreement or (ii) the period starting with the date of
filing of, and ending on the date one hundred eighty (180) days following the
effective date of the registration statement pertaining to the Initial Offering;
provided that the Company makes reasonable good faith efforts to cause such
registration statement to become effective.

                  (d) The Company shall not be required to effect a registration
pursuant to this Section 2.2:

                           (i) after the Company has effected two (2)
registrations pursuant to this Section 2.2, and such registrations have been
declared or ordered effective;

                           (ii) if, within thirty (30) days of receipt of a
written request from Initiating Holders pursuant to Section 2.2(a), the Company
gives notice to the Holders of the Company's intention to make a Public Offering
within ninety (90) days; or

                           (iii) if the Company shall furnish to Holders
requesting a registration statement pursuant to this Section 2.2, a certificate
signed by the Chairman of the Board stating that in the good faith judgment of
the Board of Directors of the Company, it would be seriously detrimental to the
Company and its stockholders for such registration statement to be effected at
such time, in which event the Company shall have the right to defer such filing
for a period of not more than ninety (90) days after receipt of the request of
the Initiating Holders; provided that such right to delay a request shall be
exercised by the Company not more than twice in any twelve (12) month period.

         2.3 PIGGYBACK REGISTRATIONS.

                  (a) The Company shall notify all Holders of Registrable
Securities in writing at least thirty (30) days prior to the filing of any
registration statement under the Securities Act for purposes of a public
offering of securities of the Company (including, but not limited to,
registration statements relating to secondary offerings of securities of the
Company, but excluding registration statements relating to employee benefit
plans or with respect to corporate reorganizations or other transactions under
Rule 145 of the Securities Act) and will afford each such Holder an opportunity
to include in such registration statement all or part of such Registrable
Securities held by such Holder. Each Holder desiring to include in any such
registration statement all or any part of the Registrable Securities held by it
shall, within fifteen (15) days after the receipt of the above-described notice
from the Company, so notify the Company in writing. Such notice shall state the
intended method of disposition of the Registrable Securities held by such
Holder. If a Holder decides not to include all of its Registrable Securities in
any registration statement thereafter filed by the Company, such Holder shall
nevertheless continue to have the right to include any Registrable Securities in
any subsequent registration statement or registration statements as may be filed
by the Company with respect to offering of its securities, all upon the terms
and conditions set forth herein.

                  (b) The Company shall notify all of the stockholders listed on
Exhibit C attached hereto in writing at least ten (10) days prior to the filing
of any registration statement

                                       6
<PAGE>

under the Securities Act for purposes of a public offering of securities of the
Company (including, but not limited to, registration statements relating to
secondary offerings of securities of the Company, but excluding registration
statements relating to employee benefit plans or with respect to corporate
reorganizations or other transactions under Rule 145 of the Securities Act) and
will afford each such stockholder an opportunity to include in such registration
statement all or part of the Common Stock of the Company held by such
stockholder. Each stockholder desiring to include in any such registration
statement all or any part of the Common Stock held by it shall, within five (5)
days after the receipt of the above-described notice from the Company, so notify
the Company in writing. Such notice shall state the intended method of
disposition of the Common Stock held by such stockholder.

                  (c) UNDERWRITING. If the registration statement under which
the Company gives notice under this Section 2.3 is for an underwritten offering,
the Company shall so advise the Holders of Registrable Securities. In such
event, the right of any such Holder to be included in a registration pursuant to
this Section 2.3 shall be conditioned upon such Holder's participation in such
underwriting and the inclusion of such Holder's Registrable Securities in the
underwriting to the extent provided herein. All Holders proposing to distribute
their Registrable Securities through such underwriting shall enter into an
underwriting agreement in customary form with the underwriter or underwriters
selected for such underwriting by the Company. Notwithstanding any other
provision of the Agreement, if the underwriter and/or the Company determine in
good faith that marketing factors require a limitation of the number of shares
to be underwritten, the number of shares that may be included in the
underwriting shall be allocated first to the Company, second, to the Holders, if
any, seeking registration under Section 2.2 hereof on a pro rata basis based on
the total number of Registrable Securities held by the Holders and third, to any
stockholder of the Company (other than a Holder) on a pro rata basis. No such
reduction shall reduce the securities being offered by the Company for its own
account to be included in the registration and underwriting, and in no event
shall the amount of securities of the selling Holders included in the
registration be reduced below thirty percent (30%) of the total amount of
securities included in such registration, unless such offering is the Initial
Offering and such registration does not include shares of any other selling
stockholders (other than the stockholder(s), if any, invoking the demand
registration) in which event any or all of the Registrable Securities of the
Holders may be excluded in accordance with the immediately preceding sentence.
In no event will shares of any other selling stockholder be included in such
registration which would reduce the number of shares which may be included by
Holders without the prior written consent of Holders of not less than two-thirds
(66.67%) of the Registrable Securities proposed to be sold in the offering,
provided, however, that in the event any securities held by the Holders are
included in a registration under this Section 2.3, other selling stockholders
shall have the right to include, on a pro rata basis based on the number of
shares held by such stockholder, up to ten percent (10%) of the number of shares
that are being registered by the Holders in such registration to the extent that
such shares may not be sold pursuant to Rule 701 or Rule 144, or any similar
exemption under the Securities Act.

                  (d) RIGHT TO TERMINATE REGISTRATION. The Company shall have
the right to terminate or withdraw any registration initiated by it under this
Section 2.3 prior to the effectiveness of such registration whether or not any
Holder has elected to include securities in such registration. The Registration
Expenses of such withdrawn registration shall be borne by the Company in
accordance with Section 2.5 hereof.

                                       7
<PAGE>

         2.4 FORM S-3 REGISTRATION. In case the Company shall receive from any
Holder or Holders of Registrable Securities a written request or requests that
the Company effect a registration on Form S-3 (or any successor to Form S-3) or
any similar short-form registration statement and any related qualification or
compliance with respect to all or a part of the Registrable Securities owned by
such Holder or Holders, the Company will:

                  (a) promptly give written notice of the proposed registration,
and any related qualification or compliance, to all other Holders of Registrable
Securities; and

                  (b) as soon as practicable, effect such registration and all
such qualifications and compliances as may be so requested and as would permit
or facilitate the sale and distribution of all or such portion of such Holder's
or Holders' Registrable Securities as are specified in such request, together
with all or such portion of the Registrable Securities of any other Holder or
Holders joining in such request as are specified in a written request given
within fifteen (15) days after receipt of such written notice from the Company;
provided, however, that the Company shall not be obligated to effect any such
registration, qualification or compliance pursuant to this Section 2.4:

                           (i) if Form S-3 (or any successor or similar form) is
not available for such offering by the Holders; or

                           (ii) if the Holders, together with the holders of any
other securities of the Company entitled to inclusion in such registration,
propose to sell Registrable Securities and such other securities (if any) at an
aggregate price to the public of less than $500,000; or

                           (iii) if the Company shall furnish to the Holders a
certificate signed by the Chairman of the Board of Directors of the Company
stating that in the good faith judgment of the Board of Directors of the
Company, it would be seriously detrimental to the Company and its stockholders
for such Form S-3 Registration to be effected at such time, in which event the
Company shall have the right to defer the filing of the Form S-3 registration
statement for a period of not more than ninety (90) days after receipt of the
request of the Holder or Holders under this Section 2.4; provided, that such
right to delay a request shall be exercised by the Company not more than twice
in any twelve (12) month period; or

                           (iv) if the Company, within any twelve (12) month
period preceding the date of such request, has already effected two (2)
registrations on Form S-3 for the Holders pursuant to this Section 2.4; or

                           (v) in any particular jurisdiction in which the
Company would be required to qualify to do business or to execute a general
consent to service of process in effecting such registration, qualification or
compliance.

                  (c) Subject to the foregoing, the Company shall file a Form
S-3 registration statement covering the Registrable Securities and other
securities so requested to be registered as soon as practicable after receipt of
the request or requests of the Holders.

                  (d) Registrations effected pursuant to this Section 2.4 shall
not be counted as demands for registration or registrations effected pursuant to
Section 2.2.

                                       8
<PAGE>

         2.5 EXPENSES OF REGISTRATION. Except as specifically provided herein,
all Registration Expenses incurred in connection with any registration,
qualification or compliance pursuant to Section 2.2 or any registration under
Section 2.3 or Section 2.4 herein shall be borne by the Company. All Selling
Expenses incurred in connection with any registrations hereunder, shall be borne
by the holders of the securities so registered pro rata on the basis of the
number of shares so registered. The Company shall not, however, be required to
pay for expenses of any registration proceeding begun pursuant to Section 2.2 or
2.4, the request of which has been subsequently withdrawn by the Initiating
Holders unless (a) the withdrawal is based upon material adverse information
concerning the Company of which the Initiating Holders were not aware at the
time of such request or (b) the Holders of a majority of Registrable Securities
agree to forfeit their right to one requested registration pursuant to Section
2.2 or Section 2.4, as applicable, in which event such right shall be forfeited
by all Holders. If the Holders are required to pay the Registration Expenses,
such expenses shall be borne by the holders of securities (including Registrable
Securities) requesting such registration in proportion to the number of shares
for which registration was requested. If the Company is required to pay the
Registration Expenses of a withdrawn offering pursuant to clause (a) above, then
the Holders shall not forfeit their rights pursuant to Section 2.2 or Section
2.4 to a demand registration.

         2.6 OBLIGATIONS OF THE COMPANY. Whenever required to effect the
registration of any Registrable Securities, the Company shall, as expeditiously
as reasonably possible:

                  (a) Prepare and file with the SEC a registration statement
with respect to such Registrable Securities and use all reasonable efforts to
cause such registration statement to become effective, and, upon the request of
the Holders of a majority of the Registrable Securities registered thereunder,
keep such registration statement effective for up to ninety (90) days or, if
earlier, until the Holder or Holders have completed the distribution related
thereto.

                  (b) Prepare and file with the SEC such amendments and
supplements to such registration statement and the prospectus used in connection
with such registration statement as may be necessary to comply with the
provisions of the Securities Act with respect to the disposition of all
securities covered by such registration statement.

                  (c) Furnish to the Holders such number of copies of a
prospectus, including a preliminary prospectus, in conformity with the
requirements of the Securities Act, and such other documents as they may
reasonably request in order to facilitate the disposition of Registrable
Securities owned by them.

                  (d) Use all reasonable efforts to register and qualify the
securities covered by such registration statement under such other securities or
Blue Sky laws of such jurisdictions as shall be reasonably requested by the
Holders, provided that the Company shall not be required in connection therewith
or as a condition thereto to qualify to do business or to file a general consent
to service of process in any such states or jurisdictions.

                  (e) In the event of any underwritten public offering, enter
into and perform its obligations under an underwriting agreement, in usual and
customary form, with the managing underwriter(s) of such offering. Each Holder
participating in such underwriting shall also enter into and perform its
obligations under such an agreement.

                                       9
<PAGE>

                  (f) Notify each Holder of Registrable Securities covered by
such registration statement at any time when a prospectus relating thereto is
required to be delivered under the Securities Act of the happening of any event
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading in the light of the circumstances then
existing.

                  (g) Furnish, at the request of a majority of the Holders
participating in the registration, on the date that such Registrable Securities
are delivered to the underwriters for sale, if such securities are being sold
through underwriters, or, if such securities are not being sold through
underwriters, on the date that the registration statement with respect to such
securities becomes effective, (i) an opinion, dated as of such date, of the
counsel representing the Company for the purposes of such registration, in form
and substance as is customarily given to underwriters in an underwritten public
offering and reasonably satisfactory to a majority in interest of the Holders
requesting registration, addressed to the underwriters, if any, and to the
Holders requesting registration of Registrable Securities and (ii) a letter
dated as of such date, from the independent certified public accountants of the
Company, in form and substance as is customarily given by independent certified
public accountants to underwriters in an underwritten public offering and
reasonably satisfactory to a majority in interest of the Holders requesting
registration addressed to the underwriters, if any, and if permitted by
applicable accounting standards, to the Holders requesting registration of
Registrable Securities.

                  (h) Cause all such Registrable Securities registered pursuant
hereunder to be listed on each securities exchange or over-the-counter market on
which similar securities issued by the Company are then listed, if applicable.

                  (i) Provide a transfer agent and registrar for such
Registrable Securities and a CUSIP number for all such Registrable Securities,
in each case not later than the effective date of such registration.

         2.7 TERMINATION OF REGISTRATION RIGHTS. All registration rights granted
under this Section 2 shall terminate and be of no further force and effect five
(5) years after the date of a Qualified Public Offering. In addition, a Holder's
registration rights shall expire if (i) the Company has completed a Qualified
Public Offering and is subject to the provisions of the Exchange Act, and (ii)
all Registrable Securities held by and issuable to such Holder and such Holder's
affiliates may be sold under Rule 144 during any ninety (90) day period without
relying on Rule 144(k).

         2.8 DELAY OF REGISTRATION; FURNISHING INFORMATION.

                  (a) No Holder shall have any right to obtain or seek an
injunction restraining or otherwise delaying any such registration as the result
of any controversy that might arise with respect to the interpretation or
implementation of this Section 2.

                  (b) It shall be a condition precedent to the obligations of
the Company to take any action pursuant to Section 2.2, 2.3 or 2.4 that the
selling Holders shall furnish to the Company such information regarding
themselves, the Registrable Securities held by them and

                                       10
<PAGE>

the intended method of disposition of such securities as shall be required to
effect the registration of their Registrable Securities.

                  (c) The Company shall have no obligation with respect to any
registration requested pursuant to Section 2.2 or Section 2.4 if the number of
shares or the anticipated aggregate offering price of the Registrable Securities
to be included in the registration does not equal or exceed the number of shares
or the anticipated aggregate offering price required to originally trigger the
Company's obligation to initiate such registration as specified in Section 2.2
or Section 2.4, whichever is applicable.

         2.9 INDEMNIFICATION. In the event any Registrable Securities are
included in a registration statement under Sections 2.2, 2.3 or 2.4:

                  (a) To the extent permitted by law, the Company will indemnify
and hold harmless each Holder, the partners, officers, directors and legal
counsel of each Holder, any underwriter (as defined in the Securities Act) for
such Holder and each person, if any, who controls such Holder or underwriter
within the meaning of the Securities Act or the Exchange Act, against any
losses, claims, damages, or liabilities (joint or several) to which they may
become subject under the Securities Act, the Exchange Act or other federal or
state law, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) arise out of or are based upon any of the following statements,
omissions or violations (collectively a "VIOLATION") by the Company: (i) any
untrue statement or alleged untrue statement of a material fact contained in
such registration statement, including any preliminary prospectus or final
prospectus contained therein or any amendments or supplements thereto, (ii) the
omission or alleged omission to state therein a material fact required to be
stated therein, or necessary to make the statements therein not misleading, or
(iii) any violation or alleged violation by the Company of the Securities Act,
the Exchange Act, any state securities law or any rule or regulation promulgated
under the Securities Act, the Exchange Act or any state securities law in
connection with the offering covered by such registration statement; and the
Company will reimburse each such Holder, partner, officer or director,
underwriter or controlling person for any legal or other expenses reasonably
incurred by them in connection with investigating or defending any such loss,
claim, damage, liability or action; provided, however, that the indemnity
agreement contained in this Section 2.9(a) shall not apply to amounts paid in
settlement of any such loss, claim, damage, liability or action if such
settlement is effected without the consent of the Company, which consent shall
not be unreasonably withheld, nor shall the Company be liable in any such case
for any such loss, claim, damage, liability or action to the extent that it
arises out of or is based upon a Violation which occurs in reliance upon and in
conformity with written information furnished expressly for use in connection
with such registration by such Holder, partner, officer, director, underwriter
or controlling person of such Holder.

                  (b) To the extent permitted by law, each Holder will, if
Registrable Securities held by such Holder are included in the securities as to
which such registration qualifications or compliance is being effected,
indemnify and hold harmless the Company, each of its directors, its officers,
and legal counsel and each person, if any, who controls the Company within the
meaning of the Securities Act or the Exchange Act, and any other Holder selling
securities under such registration statement or any of such other Holder's
partners, directors or officers or any person who controls such Holder, against
any losses, claims, damages or liabilities (joint or

                                       11
<PAGE>

several) to which the Company or any such director, officer, controlling person,
underwriter or other such Holder, or partner, director, officer or controlling
person of such other Holder may become subject under the Securities Act, the
Exchange Act or other federal or state law, insofar as such losses, claims,
damages or liabilities (or actions in respect thereto) arise out of or are based
upon any Violation, in each case to the extent (and only to the extent) that
such Violation occurs in reliance upon and in conformity with written
information furnished by such Holder under an instrument duly executed by such
Holder (or its authorized agent) and stated to be specifically for use in
connection with such registration; and each such Holder will reimburse any legal
or other expenses reasonably incurred by the Company or any such director,
officer, controlling person, underwriter or other Holder, or partner, officer,
director or controlling person of such other Holder in connection with
investigating or defending any such loss, claim, damage, liability or action if
it is finally judicially determined that there was such a Violation; provided,
however, that the indemnity agreement contained in this Section 2.9(b) shall not
apply to amounts paid in settlement of any such loss, claim, damage, liability
or action if such settlement is effected without the consent of the Holder,
which consent shall not be unreasonably withheld; provided, further, that in no
event shall any indemnity under this Section 2.9 exceed the net proceeds from
the offering received by such Holder except in the case of willful fraud of such
Holder.

                  (c) Promptly after receipt by an indemnified party under this
Section 2.9 of notice of the commencement of any action (including any
governmental action), such indemnified party will, if a claim in respect thereof
is to be made against any indemnifying party under this Section 2.9, deliver to
the indemnifying party a written notice of the commencement thereof and the
indemnifying party shall have the right to participate in, and, to the extent
the indemnifying party so desires, jointly with any other indemnifying party
similarly noticed, to assume the defense thereof with counsel mutually
satisfactory to the parties; provided, however, that an indemnified party shall
have the right to retain its own counsel, with the fees and expenses to be paid
by the indemnifying party, if representation of such indemnified party by the
counsel retained by the indemnifying party would be inappropriate due to actual
or potential differing interests between such indemnified party and any other
party represented by such counsel in such proceeding. The failure to deliver
written notice to the indemnifying party within a reasonable time of the
commencement of any such action, if materially prejudicial to its ability to
defend such action, shall relieve such indemnifying party of any liability to
the indemnified party under this Section 2.9, but the omission to so deliver
written notice to the indemnifying party will not relieve it of any liability
that it may have to any indemnified party otherwise than under this Section 2.9.

                  (d) If the indemnification provided for in this Section 2.9 is
held by a court of competent jurisdiction to be unavailable to an indemnified
party with respect to any losses, claims, damages or liabilities referred to
herein, the indemnifying party, in lieu of indemnifying such indemnified party
thereunder, shall to the extent permitted by applicable law contribute to the
amount paid or payable by such indemnified party as a result of such loss,
claim, damage or liability in such proportion as is appropriate to reflect the
relative fault of the indemnifying party on the one hand and of the indemnified
party on the other in connection with the Violation(s) that resulted in such
loss claim, damage or liability, as well as any other relevant equitable
considerations. The relative fault of the indemnifying party and of the
indemnified party shall be determined by a court of law by reference to, among
other things, whether the untrue or alleged

                                       12
<PAGE>

untrue statement of a material fact or the omission to state a material fact
relates to information supplied by the indemnifying party or by the indemnified
party and the parties' relative intent, knowledge, access to information and
opportunity to correct or prevent such statement or omission; provided, that in
no event shall any contribution by a Holder hereunder exceed the proceeds from
the offering received by such Holder except in the case of willful fraud of such
Holder.

                  (e) The obligations of the Company and Holders under this
Section 2.9 shall survive completion of any offering of Registrable Securities
in a registration statement. No Indemnifying Party, in the defense of any such
claim or litigation, shall, except with the consent of each Indemnified Party,
consent to entry of any judgment or enter into any settlement which does not
include as an unconditional term thereof the giving by the claimant or plaintiff
to such Indemnified Party of a release from all liability in respect to such
claim or litigation.

         2.10 ASSIGNMENT OF REGISTRATION RIGHTS. The rights to cause the Company
to register Registrable Securities pursuant to this Section 2 may be assigned by
a Holder to a transferee or assignee of Registrable Securities which (i) is a
subsidiary, affiliate, parent, general partner, limited partner, retired
partner, member or retired member of a Holder, (ii) is a Holder's family member,
estate, trust or other entity for the benefit of an individual Holder or such
Holder's family member, or (iii) acquires at least fifty thousand (50,000)
shares of Registrable Securities (as adjusted for stock splits and
combinations); provided, that (A) the transferor shall, within ten (10) days
after such transfer, furnish to the Company written notice of the name and
address of such transferee or assignee and the securities with respect to which
such registration rights are being assigned and (B) such transferee shall agree
to be subject to all restrictions set forth in this Agreement.

         2.11 LIMITATION ON SUBSEQUENT REGISTRATION RIGHTS. After the date of
this Agreement, the Company shall not, without the prior written consent of the
Holders of at least Sixty-Five percent (65%) of the Registrable Securities,
enter into any agreement with any holder or prospective holder of any securities
of the Company that would grant such holder registration rights senior to those
granted to the Holders hereunder; provided that, the Company may not amend the
Series B Preferred Stock Purchase Agreement, dated March 16, 2000, by and
between the Company and certain purchasers listed on Exhibit A thereto, in a way
that materially alters the terms and conditions thereof without the written
consent of Holders of a majority of the Registrable Securities.

         2.12 "MARKET STAND-OFF" AGREEMENT. If requested by the Company or the
representative of the underwriters of Common Stock (or other securities) of the
Company, each Holder shall not sell or otherwise transfer or dispose of any
Common Stock (or other securities) of the Company held by such Holder (other
than those included in the registration) for a period specified by the
representative of the underwriters not to exceed one hundred eighty (180) days
following the effective date of a registration statement of the Company filed
under the Securities Act, provided that

                  (1) such agreement shall apply only to the Company's Initial
Offering;

                                       13
<PAGE>

                  (2) all officers and directors of the Company and holders of
at least one percent (1%) of the Company's voting securities enter into similar
agreements; and

                  (3) if any stockholder that is bound by a similar agreement is
granted an early release or waiver of such restrictions by the underwriters or
the Company, then all of the Holders shall be given a corresponding
proportionate release or waiver of such restrictions by the underwriters or the
Company.

         From and after the date of this Agreement, the Company shall use its
best efforts to ensure that all holders of capital stock of the Company agree to
be bound by terms substantially similar to those set forth in this Section 2.12.

         The obligations described in this Section 2.12 shall not apply to a
registration relating solely to employee benefit plans on Form S-1 or Form S-8
or similar forms that may be promulgated in the future, or a registration
relating solely to a Commission Rule 145 transaction on Form S-4 or similar
forms that may be promulgated in the future. The Company may impose
stop-transfer instructions with respect to the shares of Common Stock (or other
securities) subject to the foregoing restriction until the end of said "market
standoff".

         2.13 SEC COMPLIANCE. During any time that the Company is subject to the
reporting requirements of the Exchange Act, the Company shall timely file all
required reports pursuant to the Exchange Act. Additionally, the Company shall
make available to Investors the information contemplated by Rule 144. At such
time that any stock held by an Investor is eligible for transfer pursuant to
Rule 144(k), the Company shall, upon the request of such Investor, remove any
restrictive legend from the applicable stock certificate at no cost to such
Investor.

SECTION 3. COVENANTS OF THE COMPANY AND INVESTORS

         3.1 BASIC FINANCIAL INFORMATION AND REPORTING.

                  (a) The Company will maintain true books and records of
account in which full and correct entries will be made of all its business
transactions pursuant to a system of accounting established and administered in
accordance with generally accepted accounting principles consistently applied,
and will set aside on its books all such proper accruals and reserves as shall
be required under generally accepted accounting principles consistently applied.

                  (b) As soon as practicable after the end of each fiscal year
of the Company, and in any event within ninety (90) days thereafter, the Company
will furnish each Investor a consolidated balance sheet of the Company, as at
the end of such fiscal year, and a consolidated statement of income and a
consolidated statement of cash flows of the Company, for such year, all prepared
in accordance with generally accepted accounting principles consistently applied
and setting forth in each case in comparative form the figures for the previous
fiscal year, all in reasonable detail. Such financial statements shall be
accompanied by a report and opinion thereon by independent public accountants of
national standing selected by the Company's Board of Directors, and a
Company-prepared comparison to the Company's operating plan for such year.

                                       14
<PAGE>

                  (c) The Company will furnish each Investor, as soon as
practicable after the end of the first, second and third quarterly accounting
periods in each fiscal year of the Company and in any event within forty-five
(45) days thereafter, a consolidated balance sheet of the Company as of the end
of each such quarterly period, and a consolidated statement of income and a
consolidated statement of cash flows of the Company for such period and for the
current fiscal year to date, prepared in accordance with generally accepted
accounting principles, with the exception that no notes need be attached to such
statements and year-end audit adjustments may not have been made.

                  (d) The Company will furnish each such Investor at least
thirty (30) days prior to the beginning of each fiscal year an annual budget and
operating plans for such fiscal year (and as soon as available, any subsequent
revisions thereto).

                  (e) The Company will furnish to each Investor within sixty
(60) days after the end of each calendar month, a preliminary consolidated and
consolidating balance sheet of the Company and its subsidiaries as of the end of
such month and preliminary consolidated and consolidating statements of income,
stockholders' equity and cash flow for such month and for the period commencing
at the end of the previous fiscal year and ending with the end of such month,
setting forth in each case in comparative form the corresponding figures for the
corresponding period of the preceding fiscal year, all in reasonable detail.

                  (f) The Company will furnish to each Investor promptly, upon
receipt thereof, any written report, so called "management letter," and any
other communication submitted to the Company or any subsidiary by its
independent public accountants relating to the business, prospects or financial
condition of the Company or any subsidiaries.

                  (g) The Company will furnish to each Investor promptly, after
the commencement thereof, notice of (i) all actions, suits and proceedings
before any court or governmental department, commission, board, bureau, agency
or instrumentality, domestic or foreign, affecting the Company (or any
subsidiary) which, if successful, would materially and adversely affect the
Company's business as then conducted; and (ii) all material defaults by the
Company or any subsidiary (whether or not declared) under any agreement for
money borrowed (unless waived or cured within applicable grace periods)

         3.2 INSPECTION RIGHTS. Each Investor shall have the right to visit and
inspect any of the properties of the Company or any of its subsidiaries, and to
discuss the affairs, finances and accounts of the Company or any of its
subsidiaries with its officers, and to review such information as is reasonably
requested all at such reasonable times and as often as may be reasonably
requested; provided, however, that the Company shall not be obligated under this
Section 3.2 with respect to a competitor of the Company or with respect to
information which the Board of Directors determines in good faith is
confidential and should not, therefore, be disclosed.

         3.3 CONFIDENTIALITY OF RECORDS. Each Investor agrees to use, and to use
its best efforts to insure that its authorized representatives use, the same
degree of care as such Investor uses to protect its own confidential information
to keep confidential any information furnished to it which the Company
identifies as being confidential or proprietary (so long as such information

                                       15
<PAGE>

is not in the public domain), except that such Investor may disclose such
proprietary or confidential information to any partner, subsidiary or parent of
such Investor for the purpose of evaluating its investment in the Company as
long as such partner, subsidiary or parent is advised of the confidentiality
provisions of this Section 3.3.

         3.4 RESERVATION OF COMMON STOCK. The Company will at all times reserve
and keep available solely for issuance and delivery upon the conversion of the
Preferred Stock, all Common Stock issuable from time to time upon such
conversion.

         3.5 STOCK VESTING. Unless otherwise approved by the Board of Directors,
all stock options and other stock equivalents issued after the date of this
Agreement to employees, directors, consultants and other service providers shall
be subject to vesting as follows: (i) twenty-five percent (25%) of such stock
shall vest at the end of the first year following the earlier of the date of
issuance or such person's services commencement date with the Company, and (ii)
seventy-five percent 75% of such stock shall vest monthly over the remaining
three (3) years.

         3.6 AFFIRMATIVE COVENANTS. The Company covenants and agrees that it
will observe the following covenants on and after the date hereof and until such
covenants terminate in accordance with the provisions herein.

                  (a) The Directors shall schedule regular meetings, which
initially shall be not less frequently than five times per year and which may be
held less frequently if agreed to by a majority of the members of the Board of
Directors. In addition to approving all material transactions, policies and
other matters normally approved by a board of directors under Delaware law, a
majority of the Board of Directors, shall approve each of the following: (i)
significant (as defined from time to time by a majority of the Company's Board
of Directors) distribution, licensing or other arrangements or contracts, (ii)
material changes in executive compensation, (iii) the annual operating plan and
budget, (iv) capital expenditures in excess of amounts indicated in the annual
plan or capital budget, (vi) searches for new senior executive officers, (vii)
establishing borrowings in excess of $1 million in the aggregate from banks or
financial institutions, and (viii) pledge by the Company of any of its assets
that result in the Company's incurring obligations in excess of $1 million in
the aggregate. The Company will use reasonable efforts to obtain directors and
officers insurance, upon a determination by a majority of the Company's Board of
Directors that such insurance is desirable. The Company will indemnify the
Directors to the maximum extent permitted under Delaware law.

                  (b) The Company will establish and maintain a Compensation
Committee of the Board of Directors. The Compensation Committee will make
recommendations to the Board of Directors for such matters as management
compensation, compensation to the Company's employees or consultants under any
benefit plans, or matters relating to the Company's option plans.

                  (c) The Company will establish and maintain an Audit
Committee.

                                       16
<PAGE>

         3.7 NEGATIVE COVENANTS. Without limiting any other covenants and
provisions hereof, the Company covenants and agrees that it will observe the
following covenants on and after the date hereof:

                  (a) No amendments shall be made to any equity incentive plan
or stock option plan of the Company without the approval or consent of a
majority of the Company's Board of Directors.

                  (b) Without the consent of a majority of the Company's Board
of Directors, the Company will not make, or permit any subsidiary to make, any
loan or advance to any person, or purchase, otherwise acquire, or permit any
subsidiary to purchase or otherwise acquire, the capital stock, assets
comprising the business of, obligations of, or any interest in, any person,
except:

                           (i) investments by the Company or a subsidiary in
evidences of indebtedness issued or fully guaranteed by the United States of
America and having a maturity of not more than one year from the date of
acquisition;

                           (ii) investments by the Company or a subsidiary in
certificates of deposit, notes, acceptances and repurchase agreements having a
maturity of not more than one year from the date of acquisition issued by a bank
organized in the United States having capital, surplus and undivided profits of
at least $50,000,000;

                           (iii) loans or advances from a subsidiary to the
Company or from a subsidiary to another subsidiary;

                           (iv) investments by the Company or a subsidiary in
A-rated or better commercial paper having a maturity of not more than one year
from the date of acquisition;

                           (v) investments in a wholly-owned subsidiary; and

                           (vi) investments by the Company or a subsidiary in
"money market" fund shares, or in "money market" accounts fully insured by the
Federal Deposit Insurance Corporation and sponsored by banks and other financial
institutions, provided that such "money market" fund or "money market" accounts
invest principally in investments of the types described in clauses (i), (ii) or
(iv) of this Section 3.7(b).

                  (c) Except as approved by a majority of the Company's Board of
Directors, the Company will not make any distributions or declare or pay any
dividends, purchase, redeem, retire, or otherwise acquire for value any of its
capital stock (or rights, options or warrants to purchase such stock) now or
hereafter outstanding, return any capital to its stockholders as such, or make
any distribution of assets to its stockholders as such, or permit any subsidiary
to do any of the foregoing, except that the subsidiaries may declare and make
payment of cash and stock dividends, return capital and make distributions of
assets to the Company, and except that nothing herein contained shall prevent
the Company:

                                       17
<PAGE>

                           (i) from effecting a stock split or declaring or
paying any dividend consisting of shares of any class of its capital stock to
the holders of shares of such class of capital stock;

                           (ii) from complying with any specific provision of
the terms of the Preferred Stock (as contained in the Certificate of
Incorporation) relating to the payment of dividends, liquidation preferences or
redemption payments on or with respect to the Preferred Stock or redemption of
the Preferred Stock;

                           (iii) from complying with the provisions of the
Certificate of Incorporation relating to redemption of the Preferred Stock; and

                           (iv) from repurchasing stock options or shares of its
Common Stock in connection with the termination of an employee, director or
consultant of the Company, the proposed transfer by an employee, director or
consultant of stock options or shares of its Common Stock or as set forth in
Section 6 or 7 hereof.

         3.8 PROPRIETARY INFORMATION AND INVENTIONS ASSIGNMENT AGREEMENTS. The
Company shall cause each current and future officer, employee and consultant of
the Company to execute and deliver a Proprietary Information and Inventions
Assignment Agreement or Consulting Contract, as applicable, substantially in the
forms attached to the Purchase Agreement.

         3.9 REGULATORY MATTERS. Each Investor agrees to cooperate with the
Company in all reasonable respects in complying with the terms and provisions of
the letter agreement between the Company and J.P. Morgan Partners (SBIC), LLC
("JP Morgan"), a copy of which is attached hereto as Exhibit D, regarding
regulatory matters (the "Regulatory Sideletter"), including without limitation,
voting to approve amending the Company's Certificate of Incorporation, the
Company's by-laws or this Agreement in a manner reasonably acceptable to the
Investors and JP Morgan or any affiliate of JP Morgan entitled to make such
request pursuant to the Regulatory Sideletter in order to remedy a Regulatory
Problem (as defined in the Regulatory Sideletter). The terms of the Regulatory
Sideletter are incorporated herein by reference. Anything contained in this
Section 3.9 to the contrary notwithstanding, no Investor shall be required under
this Section 3.9 to take any action that would adversely affect in any material
respect such Investor's rights under this Agreement or as a stockholder of the
Company. The Company and each Investor agree not to amend or waive the voting or
other provisions of the Company's Certificate of Incorporation, the Company's
by-laws or this Agreement if such amendment or waiver would cause JP Morgan or
any its Affiliates to have a Regulatory Problem (as defined in the Regulatory
Sideletter). JP Morgan agrees to notify the Company as to whether or not it
would have a Regulatory Problem promptly after JP Morgan has notice of such
amendment or waiver.

         3.10 TERMINATION OF COVENANTS. All covenants of the Company contained
in Section 3 of this Agreement (with the exception of Section 3.9) shall expire
and terminate as to each Investor on the earlier to occur of (i) the effective
date of the registration statement pertaining to a Qualified Public Offering or
(ii) following an Acquisition or Asset Transfer (as defined in the Company's
Restated Certificate of Incorporation).

                                       18
<PAGE>

SECTION 4. PREEMPTIVE RIGHTS

         4.1 SUBSEQUENT OFFERINGS. So long as a Holder (with its affiliates)
shall own at least one million four hundred thousand (1,400,000) shares of
Registrable Securities (as adjusted for stock dividends, stock splits and
combinations), such Holder shall have a preemptive right to purchase its pro
rata share of all Equity Securities that the Company may, from time to time,
propose to sell and issue after the date of this Agreement, other than the
Equity Securities excluded by Section 4.6 hereof. Each Holder's pro rata share
(the "PROPORTIONATE PERCENTAGE") is equal to the ratio of (A) the number of
shares of the Company's Common Stock (including all shares of Common Stock
issued or issuable upon conversion of the Shares) of which such Holder is deemed
to be a holder immediately prior to the issuance of such Equity Securities to
(B) the total number of shares of the Company's outstanding Common Stock on a
fully-diluted basis (including all shares of Common Stock issued or issuable
upon conversion of the Shares or upon the exercise of any outstanding warrants
or options outstanding as of the date of this Agreement; provided, however, that
such calculation shall not include any shares of Common Stock issued or issuable
upon conversion of or exercise of any securities issued after the date of this
Agreement) immediately prior to the issuance of the Equity Securities.

         4.2 EXERCISE OF RIGHTS. If the Company proposes to issue any Equity
Securities, it shall give each Holder written notice of its intention,
describing the Equity Securities, the price and the terms and conditions upon
which the Company proposes to issue the same. Each Holder shall have fifteen
(15) days from the giving of such notice to agree to purchase its pro rata share
of the Equity Securities for the price and upon the terms and conditions
specified in the notice by giving written notice to the Company and stating
therein the quantity of Equity Securities to be purchased. Notwithstanding the
foregoing, the Company shall not be required to offer or sell such Equity
Securities to any Holder who would cause the Company to be in violation of
applicable federal securities laws by virtue of such offer or sale.

         4.3 ISSUANCE OF EQUITY SECURITIES TO OTHER PERSONS. If not all of the
Holders elect to purchase their pro rata share of the Equity Securities, then
the Company shall promptly notify in writing the Holders who do so elect and
shall offer such Holders the right to acquire such unsubscribed shares. The
Holders shall have five (5) days after receipt of such notice to notify the
Company of its election to purchase all or a portion thereof of the unsubscribed
shares. If the Holders fail to exercise in full the preemptive rights, the
Company shall have sixty (60) days thereafter to sell the Equity Securities in
respect of which the Holder's rights were not exercised, at a price and upon
general terms and conditions materially no more favorable to the purchasers
thereof than specified in the Company's notice to the Holders pursuant to
Section 4.2 hereof. If the Company has not sold such Equity Securities within
sixty (60) days of the notice provided pursuant to Section 4.2, the Company
shall not thereafter issue or sell any Equity Securities, without first offering
such securities to the Holders in the manner provided above.

         4.4 TERMINATION OF PREEMPTIVE RIGHTS. The preemptive rights established
by this Section 4 shall not apply to the registration statement pertaining to a
Qualified Public Offering and shall terminate upon the closing of such Qualified
Public Offering.

                                       19
<PAGE>

         4.5 TRANSFER OF PREEMPTIVE RIGHTS. The preemptive rights of each Holder
under this Section 4 may be transferred to the same parties, subject to the same
restrictions, as any transfer of registration rights pursuant to Section 2.10.

         4.6 EXCLUDED SECURITIES. The preemptive rights established by this
Section 4 shall have no application to any of the following Equity Securities:

                  (a) shares of Common Stock (and/or options, warrants or other
Common Stock purchase rights issued pursuant to such options, warrants or other
rights) issued or to be issued to employees, officers or directors of, or
consultants or advisors to the Company or any subsidiary, pursuant to stock
purchase or stock option plans or other arrangements that are approved by the
Board of Directors;

                  (b) stock issued pursuant to any rights or agreements
outstanding as of the date of this Agreement, options and warrants outstanding
as of the date of this Agreement; and stock issued pursuant to any such rights
or agreements granted after the date of this Agreement, provided that the
preemptive rights established by this Section 4 applied with respect to the
initial sale or grant by the Company of such rights or agreements;

                  (c) any Equity Securities issued for consideration other than
cash pursuant to a merger, consolidation, acquisition or similar business
combination;

                  (d) shares of Common Stock issued in connection with any stock
split, stock dividend or recapitalization by the Company;

                  (e) shares of Common Stock issued upon conversion of the
Shares or the Series B Preferred Stock;

                  (f) any Equity Securities that are issued by the Company
pursuant to a registration statement filed under the Securities Act;

                  (g) any Equity Securities issued pursuant to any equipment
leasing arrangement, or debt financing from a bank or similar financial
institution pursuant to agreements approved by the Company's Board of Directors;
and

                  (h) any Equity Securities issued in connection with strategic
transactions involving the Company and other entities, including (i) joint
ventures, manufacturing, marketing or distribution arrangements or (ii)
technology transfer or development arrangements; provided that such strategic
transactions and the issuance of shares therein, has been approved by not less
than a majority of all of the Company's Board of Directors.

SECTION 5. RIGHT OF FIRST REFUSAL

         5.1 RIGHT OF FIRST REFUSAL. No Common Stockholder shall sell, assign,
pledge, or in any manner transfer any of the shares of the Common Stock of the
Company or any right or interest therein, whether voluntarily or by operation of
law, or by gift or otherwise, except by a transfer which meets the requirements
hereinafter set forth in this Section 5.

                                       20
<PAGE>

                  (a) If the Common Stockholder desires to sell or otherwise
transfer any of his shares of Common Stock, then the Common Stockholder shall
first give written notice thereof to the Company (the "TRANSFER NOTICE"). The
Transfer Notice shall name the proposed transferee and state the number of
shares to be transferred, the proposed consideration and all other terms and
conditions of the proposed transfer.

                  (b) For a period of twenty (20) business days following
receipt of such Transfer Notice, the Company shall have the option to purchase
all or any portion of the shares specified in the notice at the price and upon
the terms set forth in such Transfer Notice. In the event of a gift, property
settlement or other transfer in which the proposed transferee is not paying the
full price for the shares, and that is not otherwise exempted from the
provisions of this Section 5, the price shall be deemed to be the fair market
value of the stock at such time as determined in good faith by the Board of
Directors.

                  (c) Each Investor who (with their affiliates) owns at least
seven hundred fifty thousand (750,000) shares of Registrable Securities (as
adjusted for stock dividends, stock splits and combinations) (a "MAJOR
INVESTOR") shall have a right to purchase its pro rata portion of the portion of
the right of first refusal that is not exercised by the Company (the "RIGHT OF
FIRST REFUSAL"). The Company shall notify each Major Investor of such right
promptly, but in no event later than ten (10) days following the Company's
receipt of the Transfer Notice. Each Major Investor shall have the right and
option to purchase up to its pro rata share of the securities subject to such
Right of First Refusal. For purposes of this paragraph, a Major Investor's pro
rata share shall be equal to the product obtained by multiplying (i) the number
of shares subject to such Right of First Refusal by (ii) a fraction the
numerator of which is the number of shares of Common Stock owned by the Major
Investor (including all shares of the Common Stock issued or issuable upon
conversion of the Shares) and the denominator of which is the total number of
shares of Common Stock owned by the Common Stockholder and the Major Investors
at the time of the sale or transfer (including all shares of the Common Stock
issued or issuable upon conversion of the Shares). Each Major Investor who
desires to purchase securities subject to the Transfer Notice shall notify the
Company and the selling securityholder within ten (10) days of receipt of the
Transfer Notice. Any purchases made by the Major Investors pursuant to the
exercise of the foregoing right shall be made in accordance with the terms set
forth in this Section 5 and in the Transfer Notice.

                  (d) In the event that any Major Investor elects not to
purchase its full pro rata share of the securities set forth in Section 5(c)
above, then the Company shall promptly notify the Major Investors who do so
elect (the "PARTICIPATING INVESTORS" and each individually a "PARTICIPATING
INVESTOR") and shall reoffer the remaining unpurchased portion of the securities
subject to the Right of First Refusal to such Participating Investors on a pro
rata basis. For purposes of this paragraph, a Participating Investor's pro rata
share shall be equal to the product obtained by multiplying (i) the number of
shares in the unsold portion by (ii) a fraction, the numerator of which is the
number of shares of Common Stock held by such Participating Investor (including
all shares of the Company's outstanding Common Stock issued or issuable upon
conversion of the Shares) and the denominator of which is the total number of
shares of Common Stock held by such Participating Investors and the Common
Stockholder (including all shares of the Company's outstanding Common Stock
issued or issuable upon conversion of the Shares). Each such Participating
Investor shall have the right, exercisable upon written notice to

                                       21
<PAGE>

the Company and the selling securityholder within five (5) days after receipt of
such notice, to purchase all or a portion thereof of the remaining securities.

                  (e) In the event the Company and/or the Major Investors elect
to purchase all or any portion of the shares, the Company's Secretary shall give
written notice to the transferring Common Stockholder of the election and
settlement thereof shall be made in cash within thirty (30) days after the
Secretary of the Company receives said Transfer Notice; provided, that, if the
terms of payment set forth in said transferring Common Stockholder's notice were
other than cash against delivery, the Company and/or its assignee(s) shall pay
for said shares on the same terms and conditions set forth in said Transfer
Notice.

                  (f) If the Company and/or the Major Investors do not elect to
acquire all of the shares specified in the Transfer Notice, said transferring
Common Stockholder may, subject to Section 7 below, within the sixty (60)-day
period following the expiration of the option rights granted to the Company
and/or the Major Investors herein, enter into an agreement to transfer the
shares specified in said transferring Common Stockholder's notice which were not
acquired by the Company and/or the Major Investors as specified in said Transfer
Notice (the "CO-SALE STOCK"). All shares so sold by said transferring Common
Stockholder shall continue to be subject to the provisions of this Section 5 and
Section 7 in the same manner as before said transfer.

                  (g) Notwithstanding the foregoing, the Right of First Refusal
of the Major Investors shall not apply to (i) any pledge made by a Common
Stockholder pursuant to a bona fide loan transaction with a financial
institution that creates a mere security interest, (ii) any transfer to the
ancestors, descendants or spouse or to trusts for the benefit of such persons or
the Common Stockholder; or (iii) any bona fide gift; provided that in the event
of any transfer made hereunder, (A) the Common Stockholder shall inform the
Major Investors of such pledge, transfer or gift prior to effecting it and (B)
the pledgee, transferee or donee shall furnish the Major Investors with a
written agreement to be bound by and comply with all provisions of Section 5 and
Section 6. Such transferred stock shall remain subject to the terms of this
Agreement, and such pledgee, transferee or donee shall be treated as the "Common
Stockholder" for purposes of this Agreement.

                  (h) Notwithstanding the foregoing, the provisions of Section 5
shall not apply to the sale of any securities (i) to the public pursuant to a
registration statement filed with, and declared effective by, the Securities and
Exchange Commission under the Securities Act, or (ii) to the Company.

                  (i) This Agreement is subject to, and shall in no manner limit
the right of the Company to repurchase securities from the Common Stockholder at
cost pursuant to a stock restriction agreement or other agreement between the
Company and the Common Stockholder.

                  (j) Any sale or transfer, or purported sale or transfer, of
securities of the Company shall be null and void unless the terms, conditions
and provisions of this Section 5 are strictly observed and followed, and the
Company agrees it will not effect such transfer nor will it treat any alleged
transferee(s) as the holder of such shares without the written consent of a
majority in interest of the Major Investors.

                                       22
<PAGE>

         5.2 TERMINATION. The foregoing right of first refusal shall terminate
upon the closing of a Qualified Public Offering.

         5.3 LEGEND. Each Common Stockholder's certificates representing shares
of Common Stock of the Company shall bear on their face the following legend so
long as the foregoing Right of First Refusal or the restrictions in Section 6
below remain in effect:

                  THE COMPANY AND THE ORIGINAL PURCHASER OF THE SHARES
                  REPRESENTED BY THIS CERTIFICATE HAVE ENTERED INTO A CERTAIN
                  INVESTOR RIGHTS AGREEMENT WHEREBY THE SHARES ARE SUBJECT TO A
                  RIGHT OF FIRST REFUSAL AND/OR CO-SALE RIGHT IN FAVOR OF THE
                  COMPANY AND/OR OTHER STOCKHOLDERS. COPIES OF SUCH AGREEMENT
                  MAY BE OBTAINED UPON WRITTEN REQUEST TO THE SECRETARY OF THE
                  COMPANY.

SECTION 6. CO-SALE RIGHT

         6.1 SALES BY THE COMMON STOCKHOLDERS.

                  (a) After satisfying the terms of Section 5, if a Common
Stockholder proposes to sell the Co-Sale Stock pursuant to the same terms and
conditions, including the purchaser(s) as set forth in the Transfer Notice, then
such Common Stockholder shall give notice (the "NOTICE") simultaneously to the
Company and to each of the Major Investors at least ten (10) days prior to the
closing of such sale or transfer. In the event that the sale or transfer is
being made pursuant to the provisions of Sections 6.2(a) or 6.2(b) hereof, the
Notice shall state under which section the sale or transfer is being made.

                  (b) Each Major Investor shall have the right, exercisable upon
written notice to the Common Stockholder within ten (10) days after Notice, to
participate in such sale of Co-Sale Stock on the same terms and conditions (the
"CO-SALE RIGHT"). Such notice shall indicate the number of shares of Common
Stock such Major Investor (a "PARTICIPANT") wishes to sell under his or her
Co-Sale Right. To the extent one or more of the Investors exercise such Co-Sale
Right in accordance with the terms and conditions set forth below, the number of
shares of Co-Sale Stock that the Common Stockholder may sell in the transaction
shall be correspondingly reduced, unless the purchaser of the Co-Sale Stock
desires to purchase all of the shares which the Common Stockholder and the
Participants desire to sell, in which case all of such shares shall be sold to
the purchaser.

                  (c) Each Participant may sell all or any part of that number
of shares equal to the product obtained by multiplying (i) the aggregate number
of shares of Co-Sale Stock covered by the Notice by (ii) a fraction the
numerator of which is the number of shares of Common Stock owned by the
Participant at the time of the sale or transfer and the denominator of which is
the total number of shares of Common Stock owned by the Common Stockholder and
the Participants at the time of the sale or transfer.

                  (d) If any Major Investor does not elect to exercise its
Co-Sale Right fully in such Common Stockholder's sale pursuant to this Section
6, the Common Stockholder shall give

                                       23
<PAGE>

notice of such failure to the Participants who did so elect. Such notice may be
made by telephone if confirmed in writing within two days. The Participants
shall have five (5) days from the date such notice was given to agree to sell
their pro rata share of the unsold portion. For purposes of this paragraph, a
Participant's pro rata share shall be equal to the product obtained by
multiplying (i) the number of shares in the unsold portion by (ii) a fraction,
the numerator of which is the number of shares of Common Stock held by such
Participant and the denominator of which is the total number of shares of Common
Stock held by the Participants and the Common Stockholder.

                  (e) Each Participant who elects to participate in the sale
pursuant to this Section 6.1 shall effect its participation in the sale by
promptly delivering to the Common Stockholder for transfer to the prospective
purchaser one or more certificates, properly endorsed for transfer, which
represent:

                           (i) the type and number of shares of Common Stock
which such Participant elects to sell; or

                           (ii) that number of shares of Series A Preferred
Stock, Series C Preferred Stock or Series D Preferred Stock which is at such
time convertible into the number of shares of Common Stock which such
Participant elects to sell; provided, however, that if the prospective purchaser
objects to the delivery of Series A Stock or Series C Stock in lieu of Common
Stock, such Participant shall convert such Series A Stock or Series C Stock into
Common Stock and deliver Common Stock as provided in Section 6.1(e)(i) above.
The Company agrees to make any such conversion concurrent with the actual
transfer of such shares to the purchaser.

                  (f) The stock certificate or certificates that the Participant
delivers to the Common Stockholder pursuant to Section 6.1(e) shall be
transferred to the prospective purchaser in consummation of the sale of the
Common Stock pursuant to the terms and conditions specified in the Notice, and
the Common Stockholder shall concurrently therewith remit to such Participant
that portion of the sale proceeds to which such Participant is entitled by
reason of its participation in such sale. To the extent that any prospective
purchaser or purchasers prohibits such assignment or otherwise refuses to
purchase shares or other securities from a Participant exercising its rights of
co-sale hereunder, the Common Stockholder shall not sell to such prospective
purchaser or purchasers any Co-Sale Stock unless and until, simultaneously with
such sale, the Common Stockholder shall purchase such shares or other securities
from such Participant on the same terms and conditions specified in the Notice.

                  (g) The exercise or non-exercise of the Co-Sale Rights in
connection with one or more sales of Co-Sale Stock made by the Common
Stockholder shall not adversely affect their rights to participate in subsequent
sales of Co-Sale Stock subject to Section 6.1(a).

                  (h) If none of the Investors elect to participate in the sale
of the Co-Sale Stock subject to the Notice, the Common Stockholder may, not
later than sixty (60) days following delivery to the Company of the Notice,
enter into an agreement providing for the closing of the transfer of the Co-Sale
Stock covered by the Notice within thirty (30) days of such agreement on terms
and conditions not more favorable to the transferor than those described in the
Notice.

                                       24
<PAGE>

Any proposed transfer on terms and conditions more favorable than those
described in the Notice, as well as any subsequent proposed transfer of any of
the Co-Sale Stock by the Common Stockholder, shall again be subject to the
Co-Sale Rights of the Stockholders and shall require compliance by the Common
Stockholder with the procedures described in this Section 6.1.

         6.2 EXEMPT TRANSFERS.

                  (a) Notwithstanding the foregoing, the co-sale rights of the
Investors shall not apply to (i) any pledge of Co-Sale Stock made by a Common
Stockholder pursuant to a bona fide loan transaction with a financial
institution that creates a mere security interest, (ii) any transfer to the
ancestors, descendants or spouse or to trusts for the benefit of such persons or
the Common Stockholder; or (iii) any bona fide gift; provided that in the event
of any transfer made hereunder, (A) the Common Stockholder shall inform the
Investors of such pledge, transfer or gift prior to effecting it and (B) the
pledgee, transferee or donee shall furnish the Investors with a written
agreement to be bound by and comply with all provisions of Section 6.1. Such
transferred Co-Sale Stock shall remain "Co-Sale Stock" hereunder, and such
pledgee, transferee or donee shall be treated as the "Common Stockholder" for
purposes of this Agreement.

                  (b) Notwithstanding the foregoing, the provisions of Section
6.1 shall not apply to the sale of any Co-Sale Stock (i) to the public pursuant
to a registration statement filed with, and declared effective by, the
Securities and Exchange Commission under the Securities Act, or (ii) to the
Company. The Co-Sale Rights set forth in this Section 6 shall terminate upon the
closing of a Qualified Public Offering.

                  (c) This Agreement is subject to, and shall in no manner limit
the right of the Company to repurchase securities from the Common Stockholder at
cost pursuant to a stock restriction agreement or other agreement between the
Company and the Common Stockholder.

         6.3 PROHIBITED TRANSFERS.

                  (a) In the event that the Common Stockholder should sell any
Co-Sale Stock in contravention of the co-sale rights of each Major Investor
under this Agreement (a "PROHIBITED TRANSFER"), each Investor, in addition to
such other remedies as may be available at law, in equity or hereunder, shall
have the put option provided below, and the Common Stockholder shall be bound by
the applicable provisions of such option.

                  (b) In the event of a Prohibited Transfer, each Major Investor
shall have the right to sell to the Common Stockholder the type and number of
shares of Common Stock equal to the number of shares each Major Investor would
have been entitled to transfer to the purchaser under Section 6.1(c) hereof had
the Prohibited Transfer been effected pursuant to and in compliance with the
terms hereof. Such sale shall be made on the following terms and conditions:

                           (i) The price per share at which the shares are to be
sold to the Common Stockholder shall be equal to the price per share paid by the
purchaser to the Common Stockholder in the Prohibited Transfer. The Common
Stockholder shall also reimburse each Major Investor for any and all fees and
expenses, including legal fees and expenses, incurred pursuant to the exercise
or the attempted exercise of the Investor's rights under Section 6.l.

                                       25
<PAGE>

                           (ii) Within ninety (90) days after the later of the
dates on which the Major Investor (a) received notice of the Prohibited Transfer
or (b) otherwise became aware of the Prohibited Transfer, each Major Investor
shall, if exercising the option created hereby, deliver to the Common
Stockholder the certificate or certificates representing shares to be sold, each
certificate to be properly endorsed for transfer.

                           (iii) The Common Stockholder shall, upon receipt of
the certificate or certificates for the shares to be sold by an Investor,
pursuant to this Section 6.3(b), pay the aggregate purchase price therefor and
the amount of reimbursable fees and expenses, as specified in Section 6.3(b)(i),
in cash or by other means acceptable to the Investor.

                  (c) Notwithstanding the foregoing, any attempt by the Common
Stockholder to transfer Co-Sale Stock in violation of Section 6.1 hereof shall
be void and the Company agrees it will not effect such a transfer nor will it
treat any alleged transferee as the holder of such shares without the written
consent of a majority in interest of the Major Investors.

         6.4 MISCELLANEOUS.

                  (a) CONDITIONS TO EXERCISE OF RIGHTS. Exercise of the
Investors' rights under this Agreement shall be subject to and conditioned upon,
and the Common Stockholder and the Company shall use their best efforts to
assist each Major Investor in, compliance with applicable laws.

                  (b) OWNERSHIP. Each Common Stockholder represents and warrants
that he or she is the sole legal and beneficial owner of those shares of Common
Stock he or she currently holds subject to the Agreement and that no other
person has any interest (other than a community property interest) in such
shares.

SECTION 7. MISCELLANEOUS

         7.1 GOVERNING LAW. This Agreement shall be governed by and construed
under the laws of the State of Colorado as applied to agreements among Colorado
residents entered into and to be performed entirely within Colorado.

         7.2 SURVIVAL. The representations, warranties covenants, and agreements
made herein shall survive any investigation made by any Holder and the closing
of the transactions contemplated hereby. All statements as to factual matters
contained in any certificate or other instrument delivered by or on behalf of
the Company pursuant hereto in connection with the transactions contemplated
hereby shall be deemed to be representations and warranties by the Company
hereunder solely as of the date of such certificate or instrument.

         7.3 SUCCESSORS AND ASSIGNS. Except as otherwise expressly provided
herein, the provisions hereof shall inure to the benefit of, and be binding
upon, the successors, assigns, heirs, executors, and administrators of the
parties hereto and shall inure to the benefit of and be enforceable by each
person who shall be a holder of Registrable Securities from time to time;
provided, however, that prior to the receipt by the Company of adequate written
notice of the transfer of any Registrable Securities specifying the full name
and address of the transferee, the Company may deem and treat the person listed
as the holder of such shares in its records as the

                                       26
<PAGE>

absolute owner and holder of such shares for all purposes, including the payment
of dividends or any redemption price.

         7.4 SEVERABILITY. In case any provision of the Agreement shall be
invalid, illegal, or unenforceable, the validity, legality, and enforceability
of the remaining provisions shall not in any way be affected or impaired
thereby.

         7.5 AMENDMENT AND WAIVER.

                  (a) Except as otherwise expressly provided, this Agreement may
be amended or modified only upon the written consent of the Company and the
holders of at least sixty-five percent (65%) of the Registrable Securities.

                  (b) Except as otherwise expressly provided, the obligations of
the Company and the rights of the Holders under this Agreement may be waived
only with the written consent of the holders of at least sixty-five percent
(65%) of the Registrable Securities.

         7.6 DELAYS OR OMISSIONS. It is agreed that no delay or omission to
exercise any right, power, or remedy accruing to any Holder, upon any breach,
default or noncompliance of the Company under this Agreement shall impair any
such right, power, or remedy, nor shall it be construed to be a waiver of any
such breach, default or noncompliance or any acquiescence therein, or of any
similar breach, default or noncompliance thereafter occurring. It is further
agreed that any waiver, permit, consent, or approval of any kind or character on
any Holder's part of any breach, default or noncompliance under the Agreement or
any waiver on such Holder's part of any provisions or conditions of this
Agreement must be in writing and shall be effective only to the extent
specifically set forth in such writing. All remedies, either under this
Agreement, by law, or otherwise afforded to Holders, shall be cumulative and not
alternative.

         7.7 NOTICES. All notices required or permitted hereunder shall be in
writing and shall be deemed effectively given (i) upon personal delivery to the
party to be notified, (ii) when sent by confirmed telex or facsimile if sent
during normal business hours of the recipient: if not, then on the next business
day, (iii) five (5) days after having been sent by registered or certified mail,
return receipt requested, postage prepaid, or (iv) one (1) day after deposit
with a nationally recognized overnight courier, specifying next day delivery,
with written verification of receipt. All communications shall be sent to the
party to be notified at the address as set forth on the signature pages hereof
or Exhibits B or C hereto or at such other address as such party may designate
by ten (10) days advance written notice to the other parties hereto.

         7.8 ATTORNEYS' FEES. In the event that any dispute among the parties to
this Agreement should result in litigation, the prevailing party in such dispute
shall be entitled to recover from the losing party all fees, costs and expenses
of enforcing any right of such prevailing party under or with respect to this
Agreement, including without limitation, such reasonable fees and expenses of
attorneys and accountants, which shall include, without limitation, all fees,
costs and expenses of appeals.

         7.9 TITLES AND SUBTITLES. The titles of the sections and subsections of
this Agreement are for convenience of reference only and are not to be
considered in construing this Agreement.

                                       27
<PAGE>

         7.10 ADDITIONAL INVESTORS. Notwithstanding anything to the contrary
contained herein, if the Company shall issue additional shares of its Series D
Stock pursuant to the Purchase Agreement, any purchaser of such shares of Series
D Stock may become a party to this Agreement by executing and delivering an
additional counterpart signature page to this Agreement and shall be deemed an
"INVESTOR" and "HOLDER" and a party hereunder.

         7.11 COMPLETE AGREEMENT. This Agreement constitutes the entire
agreement and supersedes all other prior and contemporaneous agreements and
understandings, both written and oral, between the parties hereto with regard to
the subject matter hereof.

         7.12 COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.

         7.13 AGGREGATION OF STOCK. All shares of capital stock of the Company
held or acquired by affiliated persons (including former and current partners,
former and current members and former and current stockholders) shall be
aggregated together for the purpose of determining the availability of any
rights under this Agreement.

              [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                       28
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this THIRD AMENDED
AND RESTATED INVESTOR RIGHTS AGREEMENT as of the date set forth in the first
paragraph hereof.

COMPANY:                                     INVESTORS:

MYOGEN, INC.                                 SEQUEL LIMITED PARTNERSHIP

                                             By: Sequel Venture Partners, LLC
                                                 its General Partner

By: /s/ J. William Freytag                   By: /s/ Dan Mitchell
    -------------------------------------        -------------------------------
    J. William Freytag                           Manager
    President and Chief Executive Officer

                                             SEQUEL EURO LIMITED PARTNERSHIP

COMMON STOCKHOLDERS:                         By: Sequel Venture Partners, LLC
                                                 its General Partner

/s/ Michael R. Bristow                       By: /s/ Dan Mitchell
-----------------------------------------        -------------------------------
Michael R. Bristow                               Manager

/s/ Michael Juliano                          CROSSPOINT VENTURE PARTNERS 1997
-----------------------------------------
Michael Juliano
                                             By: /s/ Don Milder
                                                 -------------------------------
                                                 its General Partner

/s/ Leslie A. Leinwand
-----------------------------------------
Leslie A. Leinwand                           INTERWEST PARTNERS VI, LP

                                             By: /s/ Arnold Oronsky
                                                 -------------------------------
                                                 General Partner
/s/ Levin Trust
-----------------------------------------
Levin Trust

/s/ M. Benjamin Perryman                      INTERWEST INVESTORS VI, LP
-----------------------------------------
M. Benjamin Perryman
                                              By: /s/ Arnold Oronsky
                                                  ------------------------------
                                                  General Partner

/s/ Frank Stewart
-----------------------------------------
Frank Stewart

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

/s/ J. William Freytag
-----------------------------------------
J. William Freytag

                                              NEW ENTERPRISE ASSOCIATES 9,
                                              LIMITED PARTNERSHIP
/s/ Joseph L. Turner
-----------------------------------------
Joseph L. Turner                              By: NEA Partners 9,
                                                  Limited Partnership

                                              By: /s/ C. Richard Kramlich
                                                  ------------------------------
/s/ John R. Julian                                C. Richard Kramlich
-----------------------------------------         General Partner
John R. Julian

                                              NEA PRESIDENTS FUND, L.P.
/s/ Ellen Leigh Curtin
-----------------------------------------
Ellen Leigh Curtin                            By: NEA General Partners, L.P.

                                              By: /s/ C. Richard Kramlich
                                                  -----------------------------
                                                  General Partner -
                                                  C. Richard Kramlich
/s/ Richard J. Gorczynski
-----------------------------------------
Richard J. Gorczynski

                                              NEA VENTURES 1999, LIMITED
                                              PARTNERSHIP
/s/ Gordon Van Dusen
-----------------------------------------
Gordon Van Dusen
                                              By: /s/ Jacqueline Myers
                                                  ------------------------------
                                                  Vice President -
                                                  Jacqueline Myers
SAVACOR TRUST

By: /s/ Michael R. Bristow                    NEW VENTURE PARTNERS IV L.P.
    -------------------------------------

                                              By:
                                                  ------------------------------

                                              By:
                                                  ------------------------------
INVESTOCOR TRUST

By: /s/ Michael R. Bristow                    CMEA LIFE SCIENCES FUND, L.P.
    -------------------------------------

                                              By: /s/ Thomas R. Baruch
                                                  ------------------------------
                                                  General Partner
/s/ Eric N. Olson
-----------------------------------------
Eric N. Olson
                                              J.P. MORGAN PARTNERS (SBIC), LLC

                                              By: /s/ Rodney A. Ferguson
                                                  ------------------------------
                                              Its: Managing Director

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                              NEW ENTERPRISE ASSOCIATES 10,
                                              LIMITED PARTNERSHIP

                                              By: NEA Partners 10, Limited
                                                  Partnership

                                              By: /s/ C. Richard Kramlich
                                                  ------------------------------
                                                  C. Richard Kramlich -
                                                  General Partner

                                              J.P. MORGAN SECURITIES INC.

                                              By: /s/ James F. Zanze
                                                  ------------------------------

                                              Its: Managing Director
                                                  ------------------------------

                                              BVCF IV, L.P.

                                              By: J.W. Puth Associates, LLC,
                                                  its General Partner

                                              By: Brinson Venture Management,
                                                  LLC, its Attorney-in-fact

                                              By: Adams Street Partners, LLC,
                                                  as its Administrative Member

                                              By: /s/ Terry Gould
                                                  ------------------------------
                                                  Terry Gould
                                                  Partner

                                              INTERWEST PARTNERS VIII, LP

                                              By: InterWest Management Partners
                                                  VIII, LLC, its general partner

                                              By: /s/ Arnold Oronsky
                                                  ------------------------------

                                              INTERWEST INVESTORS VIII, LP

                                              By: InterWest Management Partners
                                                  VIII, LLC, its general partner

                                              By: /s/ Arnold Oronsky
                                                  ------------------------------

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                              INTERWEST INVESTORS Q VIII, LP

                                              By: InterWest Management Partners
                                                  VIII, LLC, its general partner

                                              By: /s/ Arnold Oronsky
                                                  ------------------------------

                                              PACIFIC RIM LIFE SCIENCE NO. 1
                                              INVESTMENT PARTNERSHIP

                                              By: Pacific Rim Life Science
                                                  No.1/2 Investment Partnership,
                                                  its general partner

                                              By: /s/ Masahiro Michishita
                                                  ------------------------------
                                                  Masahiro Michishita, M.D.,
                                                  Ph.D., Managing General
                                                  Partner

                                              PACIFIC RIM LIFE SCIENCE NO. 2
                                              INVESTMENT PARTNERSHIP

                                              By: Pacific Rim Life Science
                                                  No.1/2 Investment Partnership,
                                                  its general partner

                                              By: /s/ Masahiro Michishita
                                                  ------------------------------
                                                  Masahiro Michishita, M.D.,
                                                  Ph.D., Managing General
                                                  Partner

                                              HFM CHARITABLE REMAINDER TRUST

                                              By: /s/ Roy M. Jones
                                                  ------------------------------
                                                  Roy M. Jones, Authorized Agent

                                              MONTAGU NEWHALL GLOBAL PARTNERS LP

                                              By: /s/ C. Ashton Newhall
                                                  ------------------------------

                                              Name: Ashton Newhall
                                                    ----------------------------

                                              Title: General Partner
                                                     ---------------------------

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                                  /s/ David N. Low, Jr.
                                                  ------------------------------
                                                  David N. Low, Jr.

                                                  /s/ Jim F. Zanze
                                                  ------------------------------
                                                  Jim F. Zanze

                                                  /s/ Philippe McAuliffe
                                                  -----------------------------
                                                  Philippe McAuliffe

                                                  /s/ Mike Gaito
                                                  ------------------------------
                                                  Mike Gaito

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                              CHINA DEVELOPMENT INDUSTRIAL
                                              BANK INC.

                                              By: CHINA DEVELOPMENT INDUSTRIAL
                                                  BANK INC.

                                              By: /s/ Tai-ying Liu
                                                  ------------------------------
                                                  Tai-ying Liu, Chairman & CEO

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                         PERSEUS-SOROS BIOPHARMACEUTICAL
                                         FUND, LP

                                         By: Perseus-Soros Partners, LLC,
                                             General Partner
                                             By: SFM Participation, LP, Member
                                             By: SFM AH, Inc., General Partner

                                             /s/ Richard D. Holahan, Jr.
                                             ------------------------------
                                             By: Richard D. Holahan, Jr.
                                             Title: Secretary

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                              HUNT VENTURES, L.P.

                                              By: /s/ J. Fulton Murray, III
                                                  ------------------------------
                                              Name: J. Fulton Murray, III
                                                    ----------------------------
                                              Title: Managing Director

                                              SILICON VALLEY BANCVENTURES, L.P.
                                              By: Silicon Valley BancVentures,
                                                  Inc., Its General Partner

                                              By: /s/ Greg Becker
                                                  ------------------------------
                                              Name: Greg Becker
                                                    ----------------------------
                                              Title: Investment Manager
                                                     ---------------------------

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                              PACIFIC RIM CAPITAL, LLC

                                              /s/ T. Chester Wang
                                              ----------------------------------
                                              T. Chester Wang

                                              /s/ James Margolis
                                              ----------------------------------
                                              James Margolis, MD

                                              THOMAS J. TOY & CONSTANCE K. TOY,
                                              JTWROS

                                              /s/ Thomas J. Toy
                                              ----------------------------------
                                              Thomas J. Toy

                                              /s/ Constance K. Toy
                                              ----------------------------------
                                              Constance K. Toy

                                              /s/ Walter M. Narajowski
                                              ----------------------------------
                                              Walter M. Narajowski

                                              DIECK-MCGURK AND ASSOCIATES, LP

                                              By: /s/ Ronald Dieck
                                                  ------------------------------
                                                  Ronald Dieck, General Partner

                                              /s/ Daniel Ruben
                                              ----------------------------------
                                              Daniel Ruben

                                              /s/ David Pflueger
                                              ----------------------------------
                                              David Pflueger

                                              /s/ James Larrick
                                              ----------------------------------
                                              James Larrick

              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                    EXHIBIT A

                         SCHEDULE OF COMMON STOCKHOLDERS

<Table>
<S>                                    <C>
Michael R. Bristow                     654,000

Savacor Trust                          136,000

InvestoCor Trust                       453,333

Michael Juliano                        544,000

Leslie A. Leinwand                     204,000

Milton Levin                           544,000

M. Benjamin Perryman                   204,000

Frank Stewart                           51,000

J. William Freytag                     629,535

Joseph Turner                           15,000

John R. Julian                               0

Ellen Leigh Curtin                           0

Richard J. Gorzynski                    52,708

Gordon Van Dusen                        21,770

Eric N. Olson                          141,667
</Table>

<PAGE>

                                    EXHIBIT B

                              SCHEDULE OF INVESTORS

<Table>
<Caption>
INVESTOR:                                      CLASS OF SHARES PURCHASED:
---------                                      --------------------------
<S>                                            <C>
Sequel Limited Partnership                     Series A, Series C and Series D
4430 Arapahoe Avenue, Suite 220
Boulder, CO  80303

------------------------------------------     --------------------------------
Sequel Euro Limited Partnership                Series A and Series C
4430 Arapahoe Avenue, Suite 220
Boulder, CO  80303

------------------------------------------     --------------------------------
Crosspoint Venture Partners 1997               Series A and Series C
18552 MacArthur Blvd., Suite 400
Irvine, CA  92612

------------------------------------------     --------------------------------
InterWest Partners VI, L.P.                    Series A and Series C
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA  94025

------------------------------------------     --------------------------------
InterWest Investors VI, L.P.                   Series A and Series C
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA  94025

------------------------------------------     --------------------------------
New Enterprise Associates 9, Limited           Series C and Series D
Partnership
1119 St. Paul Street
Baltimore, MD 21202
Attn: Gene Trainor

------------------------------------------     --------------------------------
NEA Presidents Fund, L.P.                      Series C
1119 St. Paul Street
Baltimore, MD 21202
Attn: Gene Trainor

------------------------------------------     --------------------------------
NEA Ventures 1999, Limited Partnership         Series C
1119 St. Paul Street
Baltimore, MD 21202
Attn: Gene Trainor

------------------------------------------     --------------------------------
New Venture Partners IV L.P.                   Series C
1119 St. Paul Street
Baltimore, MD 21202

------------------------------------------     --------------------------------
CMEA Life Sciences Fund, L.P.                  Series C and Series D
One Embarcadero Center, Suite 3250
San Francisco, CA 94114
Attn:  Meryl L. Schreibstein,
       Director of Administration
--------------------------------------------------------------------------------
</Table>

<PAGE>

<Table>
<S>                                            <C>
J.P. Morgan Partners (SBIC), LLC               Series D
50 California Street, Suite 2940
San Francisco, CA  94111
Attn: Rod Ferguson

With a copy to:

J.P. Morgan Partners
Official Notices Clerk
1211 Avenue of the Americas
New York, NY 10020
Facsimile: (212) 899-3401

and

J.P. Morgan Partners (SBIC), LLC
50 California Street, Suite 2940
San Francisco, CA  94111
Attn: Shannon Horton

------------------------------------------     --------------------------------
New Enterprise Associates 10, Limited          Series D
Partnership
1119 St. Paul Street
Baltimore, MD 21202
Attn: Gene Trainor

------------------------------------------     --------------------------------
J.P. Morgan Securities Inc.                    Series D
c/o Kathy Choi
225 Bush St., 4th Floor
San Francisco, CA 94104

------------------------------------------     --------------------------------
BVCF IV, L.P.                                  Series D
c/o Adams Street Partners, LLC
209 South LaSalle Street
Chicago, IL 60604

------------------------------------------     --------------------------------
InterWest Partners VIII, L.P.                  Series D
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA  94025

------------------------------------------     --------------------------------
InterWest Investors VIII, L.P.                 Series D
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA  94025

------------------------------------------     --------------------------------
InterWest Investors Q VIII, L.P.               Series D
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA  94025
--------------------------------------------------------------------------------
</Table>

<PAGE>

<Table>
<S>                                            <C>
Pacific Rim Life Science No. 1 Investment       Series D
Partnership
(C/O) Pacific Rim Ventures Co., Ltd.
2nd Floor, Green Plaza
3-7-20 Komazawa, Setagaya-ku
Tokyo 154-0012, Japan

c/o
Daisuke Takahashi, Vice President, Pacific
Rim Ventures Co., Ltd.
2nd Floor, Green Plaza
3-7-20 Komazawa, Setagaya-ku
Tokyo 154-0012, Japan
TEL: 81-3-5779-6752
FAX: 81-3-5779-6753
dta@pacificrim-ventures.com

With a copy to:
J. Joseph Marr, MD
180 Centennial Dr.
Estes Park, CO 80517
Tel: 970-215-5700
Fax: 603-853-9202
E-mail: jmarr@pacificrim-ventures.com

------------------------------------------     --------------------------------
Pacific Rim Life Science No. 2 Investment       Series D
Partnership
(C/O) Pacific Rim Ventures Co., Ltd.
2nd Floor, Green Plaza
3-7-20 Komazawa, Setagaya-ku
Tokyo 154-0012, Japan

c/o
Daisuke Takahashi, Vice President, Pacific
Rim Ventures Co., Ltd.
2nd Floor, Green Plaza
3-7-20 Komazawa, Setagaya-ku
Tokyo 154-0012, Japan
TEL: 81-3-5779-6752
FAX: 81-3-5779-6753
dta@pacificrim-ventures.com

With a copy to:
J. Joseph Marr, MD
180 Centennial Dr.
Estes Park, CO 80517
Tel: 970-215-5700
Fax: 603-853-9202
E-mail: jmarr@pacificrim-ventures.com
--------------------------------------------------------------------------------
</Table>

<PAGE>
<Table>
<S>                                            <C>
HFM Charitable Remainder Trust                 Series D
3060 Peachtree Road NW
Nineteenth Floor
Atlanta, GA  30305
Attn: Roy M. Jones

------------------------------------------     --------------------------------
Montagu Newhall Global Partners LP             Series D
52 Upper Brook Street
London W1K 2BU
Attention:  Rupert Montagu

------------------------------------------     --------------------------------
David N. Low, Jr                               Series D
21 Deer Park Drive
Greenwich, CT 06831

------------------------------------------     --------------------------------
Jim Zanze                                      Series D
2371 Broadway
San Francisco, CA. 94115

------------------------------------------     --------------------------------
Philippe McAuliffe                             Series D
19 East 7th St., Apt. 4
New York, NY 10003

------------------------------------------     --------------------------------
Mike Gaito                                     Series D
95 Horatio Street, Apt. 4C
New York, NY 10014

------------------------------------------     --------------------------------
China Development Industrial Bank Inc.         Series D
125 Naking East Road Section 5
Overseas Business Department
Taipei, 105
Taiwan
Attn: Claire Tsai, Assistant Manager

------------------------------------------     --------------------------------
Perseus-Soros Biopharmaceutical Fund, LP       Series D
888 Seventh Avenue, 29th Floor
New York, NY  10106
Attn: Steve Elms
      Andrew N. Schiff
with a copy to:
Perseus-Soros Biopharmaceutical Fund, L.P.
c/o Soros Fund Management LLC
888 Seventh Avenue, 31st Floor
New York, NY 10106
Attention:  Richard D. Holahan, Jr., Esq.
and
Paul, Weiss, Rifkind, Wharton & Garrison
1285 Avenue of the Americas
New York, New York 10019-6064
Attention: Bruce A. Gutenplan, Esq.
--------------------------------------------------------------------------------
</Table>

<PAGE>
<Table>
<S>                                            <C>
Hunt Ventures, L.P.                            Series D
Suite 1500
1445 Ross Avenue
Dallas, TX  75202
Attn: Fulton Murray
      Tom Hurtekant, Esq.

------------------------------------------     --------------------------------
Silicon Valley BancVentures L.P.               Series D
c/o
Silicon Valley BancVentures, Inc.
Attn:  Greg Becker
3000 Sand Hill Road
Building 1, Suite 200
Menlo Park, CA 94025

------------------------------------------     --------------------------------
T. Chester Wang                                Series D
c/o Acorn Campus LLC
6 Results Way
Cupertino, CA 95014

------------------------------------------     --------------------------------
James Margolis, MD                             Series D
4701 Meridian Avenue
Suite 440, Adams Building
Miami Beach, FLA 33140

------------------------------------------     --------------------------------
Thomas J. Toy & Constance K. Toy, JTWROS       Series D
331 Parrott Drive
San Mateo, CA 94402

------------------------------------------     --------------------------------
Walter M. Narajowski                           Series D
84 Blue Lagoon
Laguna Beach, Ca. 92651

------------------------------------------     --------------------------------
Dieck-McGurk and Associates, LP                Series D
335 Lowell Avenue
Palo Alto, CA  94301
Attn: Ron Dieck and Erin McGurk

------------------------------------------     --------------------------------
Daniel Ruben                                   Series D
15233 Camarillo St.
Sherman Oaks, CA 91403

------------------------------------------     --------------------------------
David Pflueger                                 Series D
Pluris Healthcare Systems
16596 W. Bayaud Dr.
Golden, CO 80401

------------------------------------------     --------------------------------
James Larrick                                  Series D
Panorama Research
2462 Wyandotte
Mt. View, CA 94043

--------------------------------------------------------------------------------
</Table>

<PAGE>

                                    EXHIBIT C

                                  STOCKHOLDERS

Michael R. Bristow                     Frank Stewart
5 Blackmer Road                        205 Coral Way
Englewood, CO 80304                    Broomfield, CO 80020

Levin Trust                            Robert L. Roden
Cambridge Management                   800 Coral
2975 Scott Boulevard, Suite 200        Broomfield, CO 80303
Santa Clara, CA 95054

Michael Juliano                        Wayne Minobe
Six the Overlook                       13900 Berry Road
Setauket, NY 11733                     Golden, CO 80401

Phillip Goodman                        Mary V. Raynolds
2975 Scott Boulevard, Suite 210        10 Random Road
Santa Clara, CA 95054                  Englewood, CO 801110

Bermer Enterprise                      Lawrence S. Zisman
c/o W. Bruce Bercovich                 5483 East Utah Place
Kay & Merkle                           Denver, CO 80222
100 The Embarcadero, Penthouse
San Francisco, CA 94105

M. Benjamin Perryman                   Cannes Trust
5401 East Dakota, No. 10               P.O. Box 713
Denver, CO 80246                       Lambertville, NJ 08530

Leslie A. Leinwand                     Carlin S. Long
280 Cactus Court                       1745 Locust Street
Boulder, CO 80304                      Denver, CO 80220

Eric N. Olson                          A. Martin Gerdes
3219 Southwestern Boulevard            South Dakota Health Research Foundation
Dallas, TX 75225                       Cardiovascular Research Institute
                                       1400 W. 22nd Street
                                       Sioux Falls, SD 57105-1570

                                       Luisa A. Mestroni
                                       1443 Rockmont Circle
                                       Boulder, CO 80303

<PAGE>

J. David Port
2970 South Steele
Denver, CO 80201

J. William Freytag
7169 Waterford Court
Niwot, CO 80503

Joseph L. Turner
674 Cascade Drive
Golden, CO 80403

John R. Julian
337 Arapahoe
Boulder, CO 80302

Ellen Leigh Curtin
6969 West 90th Avenue, #636
Westminster, CO 80021

Richard J. Gorczynski
5225 Pinehurst Court
Boulder, CO 80301

Gordon Van Dusen
3086 Promontory Court
Boulder, CO 80304

<PAGE>
                                  MYOGEN, INC.

                             FIRST AMENDMENT TO THE
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT
                                       AND
                           WAIVER OF PREEMPTIVE RIGHTS

         Pursuant to Section 7.5 of the Third Amended and Restated Investor
Rights Agreement, by and among Myogen, Inc. (the "Company") and the Investors
and Common Stockholders named therein, dated as of August 21, 2001 (the
"Agreement"), the Company and each of the undersigned Investors and Common
Stockholders hereby agree, effective as of this 27th day of August, 2003 to the
amendment and waiver (the "Amendment") set forth below. Capitalized terms used
but not defined herein have the meanings given them in the Agreement.

                                    RECITALS

         A. The Company, the Investors and the Common Stockholders entered into
the Agreement in connection with the issuance and sale of shares of the
Company's Series D Preferred Stock pursuant to the Purchase Agreement (as
defined in the Agreement).

         B. In connection with the sale and issuance of additional shares of its
Series D Preferred Stock pursuant to that certain Series D Preferred Stock
Purchase Agreement, dated August 27th, 2003 (the "2003 Purchase Agreement"), the
Company, the Investors and the Common Stockholders wish to amend the Agreement
to provide for and accommodate the sale of additional shares of its Series D
Preferred Stock pursuant to the 2003 Purchase Agreement and the holders of
Registrable Securities wish to waive any right of first refusal or preemptive
right, including notice, any Holder may have with respect to the shares of
Series D Preferred Stock sold pursuant to the 2003 Purchase Agreement.

                                    AGREEMENT

The Company and the holders of Registrable Securities hereby agree as follows:

         1. The portion of Section 1.2 setting forth the definition of
"Qualified Public Offering" is hereby amended and restated to read in its
entirety as set forth below:

                  ""QUALIFIED PUBLIC OFFERING" means the closing of a firmly
         underwritten public offering pursuant to an effective registration
         statement under the Securities Act covering the offer and sale of
         Common Stock for the account of the Company in which in which (i) the
         per share price is at least one and one-half (1.5) times the Original
         Issue Price (as adjusted for stock splits, dividends, recapitalizations
         and the like) and (ii) the cash proceeds to the Company (after
         underwriting discounts, commissions and fees) are at least
         $25,000,000."

         2. A new subsection (i) is added to Section 4.6, to read in its
entirety as set forth below:

                  "(i) any Equity Securities issued pursuant to that certain
         Series D Preferred Stock Purchase Agreement, by and among the Company
         and the Purchasers set forth on Exhibit A thereto, dated on or about
         August 27th, 2003.

         3. Section 3.10 shall be renumbered as Section 3.11, and a new Section
3.10 is added, to read in its entirety as set forth below:

                                       1.
<PAGE>

                  "3.10 REAL PROPERTY HOLDING CORPORATION NOTICE. The Company
         shall provide prompt notice to New Enterprise Associates 10, Limited
         Partnership ("NEA 10") following any "determination date" (as defined
         in Treasury Regulation Section 1.897-2(c)(1)) on which the Company
         becomes a United States real property holding corporation. In addition,
         upon a written request by NEA 10, the Company shall provide NEA 10 with
         a written statement informing NEA 10 whether NEA 10's interest in the
         Company constitutes a United States real property interest. The
         Company's determination shall comply with the requirements of Treasury
         Regulation Section 1.897-2(h)(1) or any successor regulation, and the
         Company shall provide timely notice to the Internal Revenue Service, in
         accordance with and to the extent required by Treasury Regulation
         Section 1.897-2(h)(2) or any successor regulation, that such statement
         has been made. The Company's written statement to NEA 10 shall be
         delivered to NEA 10 within 10 days of NEA 10's written request
         therefor. The Company's obligation to furnish such written statement
         shall continue notwithstanding the fact that a class of the Company's
         stock may be regularly traded on an established securities market or
         the fact that there is no preferred stock then outstanding."

         4. The undersigned holders of Registrable Securities, hereby waive on
behalf of themselves and each and every Holder, the Holders' preemptive right
pursuant to Section 4 of the Agreement to purchase shares of the Series D
Preferred Stock sold pursuant to the 2003 Purchase Agreement, and further waive
compliance by the Company with all provisions of Section 4 of the Agreement,
including the notice provisions with respect to the sale of such shares.

         5. This Amendment may be executed in any number of counterparts, each
of which may be executed by less than all of the parties hereto and each of
which shall constitute one and the same instrument.

         6. The undersigned Purchasers consent to a restatement of the Agreement
to incorporate this Amendment.

         7. This Amendment shall be effective upon its execution by the Company
and the holders of sixty-five percent (65%) of the Registrable Securities.

         8. The Amendment shall be governed and construed in accordance with the
laws of the State of Colorado as though made solely among residents of the State
of Colorado without regard to conflicts of law principals.

                      FIRST AMENDMENT TO THE MYOGEN, INC.
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                       2.

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this FIRST AMENDMENT TO THE
THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT as of the date set forth in
the first paragraph hereof.

COMPANY:                                   INVESTORS:

MYOGEN, INC.                               SEQUEL LIMITED PARTNERSHIP

                                           By: Sequel Venture Partners, LLC
                                               its General Partner

By: /s/ J. William Freytag                 By: /s/ Daniel J. Mitchell
   --------------------------                 ----------------------------------
   J. William Freytag                         Manager
   President and Chief
   Executive Officer

COMMON STOCKHOLDERS:                       SEQUEL LIMITED PARTNERSHIP III

                                           By: Sequel Venture Partners, LLC
                                               its General Partner

                                           By: /s/ Daniel J. Mitchell
-----------------------------                 ----------------------------------
Michael R. Bristow                            Manager

SAVACOR TRUST                              SEQUEL EURO LIMITED PARTNERSHIP

                                           By: Sequel Venture Partners, LLC
                                               its General Partner

By:
   --------------------------              By: /s/ Daniel J. Mitchell
                                              ----------------------------------
                                              Manager

INVESTOCOR TRUST                           SEQUEL ENTREPRENEURS' FUND III, L.P.

                                           By: Sequel Venture Partners, LLC
                                               its General Partner

By:                                        By: /s/ Daniel J. Mitchell
   --------------------------                 ----------------------------------
                                              Manager

                      FIRST AMENDMENT TO THE MYOGEN, INC.
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

J. WILLIAM FREYTAG TRUST,                      INTERWEST PARTNERS VIII, LP
IRREVOCABLE TRUST OF JENNIFER FREYTAG,         By: InterWest Management Partners
IRREVOCABLE TRUST OF KATHERINE FREYTAG,            VIII, LLC,
J. WILLIAM FREYTAG AND JANET S. FREYTAG,              Its General Partner
TRUSTEES

By: /s/ J. William Freytag                     By: /s/ Arnold Oronsky
   -------------------------------------          ------------------------------
       J. William Freytag, Trustee

                                               INTERWEST PARTNERS VI, LP

                                               By: InterWest Management Partners
                                                   VI, LLC
                                                      Its General Partner

----------------------------------------
Leslie A. Leinwand                             By: /s/ Arnold Oronsky
                                                  ------------------------------

                                               INTERWEST INVESTORS VIII, LP

                                               By: InterWest Management Partners
                                                   VIII, LLC
                                                      Its General Partner

                                               By: /s/ Arnold Oronsky
----------------------------------------          ------------------------------
Levin Trust
                                               INTERWEST INVESTORS VI, LP

                                               By: InterWest Management Partners
                                                   VIII, LLC
                                                      Its General Partner

                                               By: /s/ Arnold Oronsky
----------------------------------------          ------------------------------
M. Benjamin Perryman
                                               INTERWEST INVESTORS Q VIII, LP

                                               By: InterWest Management Partners
                                                   VIII, LLC
                                                      Its General Partner

----------------------------------------
Frank Stewart                                  By: /s/ Arnold Oronsky
                                                  ------------------------------

                      FIRST AMENDMENT TO THE MYOGEN, INC.
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                       2.

<PAGE>
                                             CROSSPOINT VENTURE PARTNERS 1997

                                             By:
                                                --------------------------------
                                                its General Partner
---------------------------------
Michael Juliano
                                             NEA VENTURES 1999, LIMITED
                                             PARTNERSHIP

                                             By: /s/ Diane N. Williams
/s/ Joseph L. Turner                            --------------------------------
---------------------------------               Vice President
Joseph L. Turner
                                             NEW VENTURE PARTNERS IV L.P.

                                             By:
                                                --------------------------------

                                             By:
---------------------------------               --------------------------------
John R. Julian
                                             NEW ENTERPRISE ASSOCIATES 10,
                                             LIMITED PARTNERSHIP

                                             By: NEA Partners 10, Limited
                                             Partnership
---------------------------------
Ellen Leigh Curtin                           By: /s/ C. Richard Kramlich
                                                --------------------------------
                                                General Partner

                                             NEW ENTERPRISE ASSOCIATES 9,
                                             LIMITED PARTNERSHIP

                                             By: NEA Partners 9, Limited
                                             Partnership
---------------------------------
Richard J. Gorczynski                        By: /s/ C. Richard Kramlich
                                                --------------------------------
                                                General Partner

                                             NEA PRESIDENTS FUND, L.P.

                                             By: NEA General Partners
---------------------------------
Gordon Van Dusen                             By: /s/ C. Richard Kramlich
                                                --------------------------------
                                                General Partner

                      FIRST AMENDMENT TO THE MYOGEN, INC.
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                       3.
<PAGE>

                                             J.P. MORGAN PARTNERS (SBIC), LLC

                                             By: /s/ Rodney A. Ferguson
---------------------------------               --------------------------------
Eric N. Olson                                Its: Rodney A. Ferguson
                                                 -------------------------------

                                             J.P. MORGAN SECURITIES INC.

                                             By:
                                                --------------------------------
                                             Its:
                                                 -------------------------------

                                             CHINA DEVELOPMENT INDUSTRIAL BANK
                                             INC.

                                             By:
                                                --------------------------------
                                             Name:
                                                  ------------------------------
                                             Title:
                                                   -----------------------------

                                             PERSEUS-SOROS BIOPHARMACEUTICAL
                                             FUND, LP

                                             By: Perseus-Soros Partners, LLC,
                                             It's General Partner
                                             By: SFM Participation, L.P., Its
                                             Managing Member
                                             By: SFM AH, LLC., Its General
                                             Partner
                                             By: Soros Private Funds Management
                                                 LLC, Its Managing Member

                                             By: /s/ Jodye M. Anzalotta
                                                --------------------------------
                                             Name: Jodye M. Anzalotta
                                                  ------------------------------
                                             Title: Attorney-in-Fact

                                             CMEA LIFE SCIENCES FUND, L.P.

                                             By: /s/ Thomas R. Baruch
                                                --------------------------------
                                                General Partner

                      FIRST AMENDMENT TO THE MYOGEN, INC.
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                       4.
<PAGE>

                                            BVCF IV, L.P.
                                            By: J.W. Puth Associates, LLC, its
                                                General Partner
                                            By: Brinson Venture Management,
                                                LLC, it's Attorney-in-fact
                                            By: Adams Street Partners, LLC, as
                                                its Administrative Member

                                            By: /s/ Craig S. Taylor
                                               --------------------------------
                                               Craig S. Taylor
                                               Partner

                                            PACIFIC RIM LIFE SCIENCE NO. 1
                                            INVESTMENT PARTNERSHIP

                                            By: Pacific Rim Life Science No.1/2
                                                Investment Partnership, its
                                                general partner

                                            By: /s/ Masahiro Michishita
                                               --------------------------------
                                               Masahiro Michishita, M.D., Ph.D.,
                                               Managing General Partner

                                            PACIFIC RIM LIFE SCIENCE NO. 2
                                            INVESTMENT PARTNERSHIP

                                            By: Pacific Rim Life Science No.1/2
                                                Investment Partnership, its
                                                general partner

                                            By: /s/ Masahiro Michishita
                                               --------------------------------
                                               Masahiro Michishita, M.D., Ph.D.,
                                               Managing General Partner

                                            MONTAGU NEWHALL GLOBAL PARTNERS LP

                                            By: /s/ C. Ashton Newhall
                                               --------------------------------
                                            Name: C. Ashton Newhall
                                                 ------------------------------
                                            Title: General Partner
                                                  -----------------------------

                      FIRST AMENDMENT TO THE MYOGEN, INC.
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                       5.
<PAGE>

                                           HUNT VENTURES

                                           By: /s/ Christopher W. Kleinert
                                              --------------------------------
                                           Name: Christopher W. Kleinert
                                                ------------------------------
                                           Title: Managing Director
                                                 -----------------------------

                                           SILICON VALLEY BANCVENTURES

                                           By: Silicon Valley BancVentures, L.P.
                                           Its General Partner

                                           By: /s/ Aaron Gershenberg
                                              --------------------------------
                                           Name: Aaron Gershenberg
                                                ------------------------------
                                           Title: Managing Director
                                                 -----------------------------

                                           HFM CHARITABLE REMAINDER TRUST

                                           By:
                                              --------------------------------
                                              Roy M. Jones, Authorized Agent

                                           -----------------------------------
                                           DAVID N. LOW, JR.

                                           -----------------------------------
                                           JIM F. ZANZE

                                           -----------------------------------
                                           PHILIPPE MCAULIFFE

                                           -----------------------------------
                                           MIKE GAITO

                                           PACIFIC RIM CAPITAL, LLC

                                           By:
                                              --------------------------------
                                              T. Chester Wang

                      FIRST AMENDMENT TO THE MYOGEN, INC.
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                       6.
<PAGE>

                                             -----------------------------------
                                             JAMES MARGOLIS, MD

                                             THOMAS J. TOY & CONSTANCE K. TOY,
                                                      JTWROS

                                             -----------------------------------
                                                Thomas J. Toy

                                             -----------------------------------
                                                Constance K. Toy

                                             -----------------------------------
                                                    WALTER M. NARAJOWSKI

                                             DIECK-MCGURK AND ASSOCIATES, LP

                                             By:
                                                --------------------------------
                                                Ronald Dieck, General Partner

                                             -----------------------------------
                                                    DANIEL RUBEN

                                             -----------------------------------
                                                    DAVID PFLUEGER

                                             -----------------------------------
                                                    JAMES LARRICK

                      FIRST AMENDMENT TO THE MYOGEN, INC.
              THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                       7.<PAGE>
                                                                    EXHIBIT 10.9

                           THIRD AMENDED AND RESTATED
                             STOCKHOLDERS AGREEMENT

         THIS THIRD AMENDED AND RESTATED STOCKHOLDERS AGREEMENT (the
"AGREEMENT") is made and entered into this 21st day of August, 2001, by and
among MYOGEN, INC., a Delaware corporation (the "COMPANY"), THOSE CERTAIN
HOLDERS OF THE COMPANY'S COMMON STOCK LISTED ON EXHIBIT A hereto (the "KEY
STOCKHOLDERS") and THE PERSONS AND ENTITIES LISTED ON EXHIBIT B hereto (the
"INVESTORS" and, together with the Key Stockholders, the "STOCKHOLDERS"). All
terms not otherwise defined herein shall have the meaning ascribed to them in
that certain Third Amended and Restated Investor Rights Agreement of even date
herewith.

                                   WITNESSETH

         WHEREAS, the Key Stockholders are the beneficial owners of an aggregate
of 3,651,013 shares of the Common Stock of the Company;

         WHEREAS, the Company sold shares of Series A Preferred Stock (the
"SERIES A STOCK") to certain Investors pursuant to the Series A Preferred Stock
Purchase Agreement dated September 23, 1998;

         WHEREAS, the Company sold shares of its Series C Preferred Stock (the
"SERIES C STOCK") to certain Investors pursuant to the Series C Preferred Stock
Purchase Agreement dated November 23, 1999;

         WHEREAS, the Company proposes to sell shares of its Series D Preferred
Stock (the "SERIES D STOCK," and together with the Series A Stock and Series C
Stock, the "SENIOR PREFERRED") to certain Investors pursuant to the Series D
Preferred Stock Purchase Agreement (the "PURCHASE AGREEMENT") of even date
herewith (the "FINANCING");

         WHEREAS, the Company granted voting rights and certain other rights
pursuant to that certain Second Amended and Restated Shareholders Agreement,
dated November 23, 1999 (the "PRIOR AGREEMENT"); and

         WHEREAS, in connection with the consummation of the Financing, the
Company, the Key Stockholders and the Investors have agreed to provide for the
future voting of their shares of the Company's capital stock as set forth below
and the Company and the parties to the Prior Agreement are willing to amend the
right given to them pursuant to the Prior Agreement by replacing such rights in
their entirety with the rights set forth in this Agreement.

         NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

                                       1
<PAGE>

                                   ARTICLE 1

                                     VOTING

         1.1 COMMON SHARES; INVESTOR SHARES.

                  (a) The Key Stockholders each agree to hold all shares of
voting capital stock of the Company registered in their respective names or
beneficially owned by them as of the date hereof, and any and all other
securities of the Company legally or beneficially acquired by each of the Key
Stockholders after the date hereof, (hereinafter collectively referred to as the
"COMMON SHARES") subject to, and to vote the Common Shares in accordance with,
the provisions of this Agreement.

                  (b) The Investors each agree to hold all shares of voting
capital stock of the Company now owned or hereinafter acquired by them
(including but not limited to all shares of Common Stock issued upon conversion
of the Senior Preferred) registered in their respective names or beneficially
owned by them as of the date hereof (and any and all other securities of the
Company legally or beneficially acquired by each of the Investors after the date
hereof) (hereinafter collectively referred to as the "INVESTOR SHARES") subject
to, and to vote the Investor Shares in accordance with, the provisions of this
Agreement.

         1.2 VOTING. From and after the date hereof and until this Agreement is
terminated as specified by Article 2, each Stockholder will vote all of his, her
or its voting securities of the Company (the "STOCKHOLDER SHARES") and take all
other necessary or desirable actions within his, her or its control (whether in
the capacity of stockholder, director, member of the executive committee or
officer of the Company or otherwise), in order to accomplish the following:

                           (i) Cause the Board to consist of not more than eight
(8) members (except if such increase is approved by the requisite vote of
stockholders of the Company in accordance with Article III, Section
C(2)(b)(viii) of the Company's Restated Certificate of Incorporation in effect
on the date hereof, as may be amended from time to time) with no Board Committee
having all the authority of the Board; and

                           (ii) If necessary for the election of such
individuals to the Board, vote all of his, her or its Stockholder Shares in
favor of the following persons:

                                    (1) two (2) people (each a "COMMON
DESIGNEE") designated by the Key Stockholders holding a majority of the Common
Shares held by the Key Stockholders, one of whom shall be the chief executive
officer of the Company (the Common Designees shall initially be J. William
Freytag and Michael Bristow).

                                    (2) one (1) person (the "SERIES A DESIGNEE")
designated by the Stockholders holding a majority of the Series A Stock (the
Series A Designee shall initially be Dan Mitchell).

                                    (3) two (2) people (each a "SERIES C
DESIGNEE") designated by the Stockholders holding a majority of the Series C
Stock (the Series C Designees shall initially be Sigrid Van Bladel and Arnold L.
Oronsky).

                                       2
<PAGE>

                                    (4) three (3) people (each a "SERIES D
DESIGNEE") designated by the Stockholders holding a majority of the Series D
Stock, one of whom shall be nominated by J.P. Morgan Partners (SBIC), LLC or its
affiliates (the "J.P. MORGAN NOMINEE") and one of whom shall be an experienced
pharmaceutical executive. The J.P. Morgan Nominee shall initially be Rodney
Ferguson, and the other two Series D Designees shall be selected after the date
of the Financing.

         1.3 REMOVAL. No director designated and elected as provided in Section
1.2 may be removed without the written consent of such Stockholders as are
entitled to designate and elect such director under Section 1.2, and any vote
taken to fill any vacancy created by the resignation, removal or death of a
director elected pursuant to Section 1.2 shall also be subject to the provisions
of Section 1.2.

         1.4 EXPENSES. The Company agrees to reimburse the designated directors
for all reasonable travel expenses incurred by such directors in connection with
any Board of Directors meetings.

         1.5 DRAG-ALONG RIGHTS. In the event that the Board of Directors of the
Company and the holders of a majority of the Stockholder Shares (the "REQUISITE
HOLDERS"), approve an Acquisition or Asset Transfer, as defined in the Company's
Restated Certificate of Incorporation, as in effect on the date hereof (an
"APPROVED Sale"), whether by means of a merger, consolidation, or sale of stock
or assets, or otherwise (each, a "SALE OF THE COMPANY"), all Stockholders shall
consent to and raise no objections against the Approved Sale, and if the
Approved Sale is structured as (i) a merger or consolidation of the Company, or
a sale of all or substantially all of the Company's assets, each Stockholder
shall waive any dissenters' rights, appraisal rights or similar rights in
connection with such merger, consolidation or asset sale or (ii) a sale of the
stock of the Company, each Stockholder shall agree to sell his or its
Stockholder Shares on the terms and conditions approved by the Requisite
Holders; provided that:

                           (i) such terms do not provide that the Stockholders
would receive less than the amount that would be distributed to such
Stockholders in the event the proceeds of the Sale of the Company were
distributed in accordance with the Company's Restated Certification of
Incorporation;

                           (ii) if any Stockholder is given an option as to the
form and amount of consideration to be received, all Stockholders will be given
the same option; and

                           (iii) no Stockholder shall be obligated to make any
out-of-pocket expenditure prior to the consummation of the Approved Sale
(excluding modest expenditures for its or his own postage, copies, etc. and the
fees and expenses of its or his own counsel retained by it), and no Stockholder
shall be obligated to pay more than its, her or his pro rata share (based upon
the number of shares of capital stock held by such Stockholder) of reasonable
expenses incurred in connection with such Approved Sale to the extent such costs
are incurred for the benefit of all Stockholders and are not otherwise paid by
the Company or the acquiring party (costs incurred by or on behalf of a
Stockholder for its or his sole benefit will not be considered costs of the
transaction hereunder).

                                       3
<PAGE>

         1.6 LEGEND.

                  (a) Concurrently with the execution of this Agreement, there
shall be imprinted or otherwise placed, on certificates representing the Common
Shares and the Investor Shares the following restrictive legend (the "LEGEND"):

                  "THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO THE
                  TERMS AND CONDITIONS OF A STOCKHOLDERS AGREEMENT WHICH PLACES
                  CERTAIN RESTRICTIONS ON THE VOTING OF THE SHARES REPRESENTED
                  HEREBY. ANY PERSON ACCEPTING ANY INTEREST IN SUCH SHARES SHALL
                  BE DEEMED TO AGREE TO AND SHALL BECOME BOUND BY ALL THE
                  PROVISIONS OF SUCH AGREEMENT. A COPY OF SUCH STOCKHOLDERS
                  AGREEMENT WILL BE FURNISHED TO THE RECORD HOLDER OF THIS
                  CERTIFICATE WITHOUT CHARGE UPON WRITTEN REQUEST TO MYOGEN,
                  INC., AT ITS PRINCIPAL PLACE OF BUSINESS."

                  (b) The Company agrees that, during the term of this
Agreement, it will not remove, and will not permit to be removed (upon
registration of transfer, reissuance or otherwise), the Legend from any such
certificate and will place or cause to be placed the Legend on any new
certificate issued to represent Common Shares or Investor Shares theretofore
represented by a certificate carrying the Legend.

         1.7 SUCCESSORS. Prior to transferring any Common Shares or Investor
Shares to any person the transferring Stockholder will cause the prospective
transferee to execute and deliver to the Company and to the other Stockholders
an agreement similar to this Agreement in form and substance. The provisions of
this Agreement shall be binding upon the successors in interest to any of the
Common Shares or Investor Shares. The Company shall not permit the transfer of
any of the Common Shares or Investor Shares on its books or issue a new
certificate representing any of the Common Shares or Investor Shares unless and
until the person to whom such security is to be transferred shall have executed
a written Agreement, substantially in the form of this Agreement, pursuant to
which such person becomes a party to this Agreement and agrees to be bound by
all the provisions hereof as if such person were a Key Stockholder or Investor,
as applicable.

         1.8 OBSERVER. CMEA Life Sciences Fund, L.P. ("CMEA") may have one
representative attend meetings of the Company's Board of Directors in a
non-voting capacity; provided that such CMEA representative signs the Company's
form non-disclosure agreement in the form provided by the Company not to
disclose the matters discussed at such meetings, and that the Company shall have
the right to exclude such representative from a portion of any meeting as the
Company and its counsel reasonably deems necessary to protect the Company's
attorney-client privilege.

                                       4
<PAGE>

         1.9 OTHER RIGHTS. Except as provided by this Agreement, each Key
Stockholder and Investor shall exercise the full rights of a stockholder of the
Company with respect to the Common Shares and the Investor Shares, respectively.

                                   ARTICLE 2

                                   TERMINATION

         2.1 This Agreement shall continue in full force and effect from the
date hereof through the earliest of the following dates, on which it shall
terminate in its entirety:

                  (a) the date of the closing of a firm commitment underwritten
public offering of the Company's Common Stock registered under the Securities
Act of 1933, as amended, which results in the Senior Preferred being converted
into Common Stock;

                  (b) the date of the closing of a merger, reorganization or
consolidation of the Company in which the holders of outstanding voting
securities of the Company immediately prior to such merger, reorganization or
consolidation do not hold a majority of the voting securities of the surviving
entity outstanding immediately after such merger, reorganization or
consolidation other than the Financing;

                  (c) ten (10) years from the date of this Agreement; or

                  (d) the date as of which the parties hereto terminate this
Agreement by written consent of a majority in interest of the Investors and a
majority in interest of the Key Stockholders; provided, however, that in the
event at least sixty-five percent (65%) of the outstanding shares of Senior
Preferred voting together as a class (on an as-if converted to Common Stock
basis) exercises the redemption right set forth in Section 5 of the Company's
Restated Certificate of Incorporation dated as of the date hereof, this
Agreement shall terminate on the thirtieth (30th) day after the date of the
Notice described in Section 5 of the Company's Restated Certificate of
Incorporation; provided that this Agreement shall not terminate until the
Company has redeemed at least 65% of the Senior Preferred subject to such
redemption pursuant to the terms of the Restated Certificate of Incorporation.

                                   ARTICLE 3

                                  MISCELLANEOUS

         3.1 AMENDMENT AND RESTATEMENT OF PRIOR AGREEMENT. All of the
undersigned parties who were parties to the Prior Agreement and who constitute
the requisite parties to amend the Prior Agreement hereby, on behalf of
themselves and all others, agree that the Prior Agreement is null and void and
superseded in all respects by this Agreement.

         3.2 OWNERSHIP. Each Key Stockholder represents and warrants to the
Investors that (a) he or it now owns the Common Shares, free and clear of liens
or encumbrances, and has not, prior to or on the date of this Agreement,
executed or delivered any proxy or entered into any other voting agreement or
similar arrangement other than one which has expired or terminated prior to the
date hereof, and (b) such Key Stockholder has full power and capacity to
execute,

                                       5
<PAGE>

deliver and perform this Agreement which has been duly executed and delivered
by, and evidences the valid and binding obligation of, such Key Stockholder
enforceable in accordance with its terms.

         3.3 FURTHER ACTION. If and whenever the Common Shares are sold, the Key
Stockholders or the personal representative of the Key Stockholders shall do all
things and execute and deliver all documents and make all transfers, and cause
any transferee of the Common Shares to do all things and execute and deliver all
documents, as may be necessary to consummate such sale consistent with this
Agreement.

         3.4 SPECIFIC PERFORMANCE. The parties hereto hereby declare that it is
impossible to measure in money the damages which will accrue to a party hereto
or to their heirs, personal representatives, or assigns by reason of a failure
to perform any of the obligations under this Agreement and agree that the terms
of this Agreement shall be specifically enforceable. If any party hereto or his
heirs, personal representatives, or assigns institute any action or proceeding
to specifically enforce the provisions hereof, any person against whom such
action or proceeding is brought hereby waives the claim or defense therein that
such party or such personal representative has an adequate remedy at law, and
such person shall not offer in any such action or proceeding the claim or
defense that such remedy at law exists.

         3.5 GOVERNING LAW. This Agreement, and the rights of the parties
hereto, shall be governed by and construed in accordance with the laws of the
State of Colorado as such laws apply to agreements among Colorado residents made
and to be performed entirely within the State of Colorado.

         3.6 AMENDMENT. No modification, amendment or waiver of any provision of
this Agreement will be effective unless approved in a writing signed by the
Company, of Sixty-Five percent (65%) in interest of the Investors and a majority
in interest of the Key Stockholders; provided, however, that notwithstanding the
foregoing, any provision of Section 1.2(ii)(4) regarding J.P. Morgan Partners
(SBIC), LLC or its affiliates shall not be amended or waived without the written
consent of J.P. Morgan Partners (SBIC), LLC. The failure of any party to enforce
any of the provisions of this Agreement will in no way be construed as a waiver
of such provision and will not affect the right of such party thereafter to
enforce each and every provision of this Agreement in accordance with its terms.

         3.7 SEVERABILITY. Whenever possible, each provision of this Agreement
will be interpreted in such manner as to be effective and valid under applicable
law, but if any provision of this Agreement is held to be invalid, illegal or
unenforceable in any respect under any applicable law or rule in any
jurisdiction, such invalidity, illegality or unenforceability will not affect
any other provision and this Agreement shall be reformed, construed and enforced
as if such invalid, illegal or unenforceable provision had never been contained
herein.

         3.8 SUCCESSORS. This Agreement shall inure to the benefit of and be
binding upon the parties hereto and their respective heirs, successors, assigns,
administrators, executors and other legal representatives.

                                       6
<PAGE>

         3.9 ADDITIONAL SHARES. In the event that subsequent to the date of this
Agreement any shares or other securities (other than any shares or securities of
another corporation issued to the Company's stockholders pursuant to a plan of
merger) are issued on, or in exchange for, any of the Common Shares or Investor
Shares by reason of any stock dividend, stock split, consolidation of shares,
reclassification or consolidation involving the Company, such shares or
securities shall be deemed to be Common Shares or Investor Shares, as the case
may be, for purposes of this Agreement.

         3.10 ADDITIONAL INVESTORS. Notwithstanding anything to the contrary
contained herein, if the Company shall issue additional shares of its Series D
Stock pursuant to the Purchase Agreement, any purchaser of such shares of Series
D Stock may become a party to this Agreement by executing and delivering an
additional counterpart signature page to this Agreement and shall be deemed an
"INVESTOR" and a party hereunder.

         3.11 ATTORNEYS' FEES. In the event that any suit or action is
instituted to enforce any provision in this Agreement, the prevailing party
shall be entitled to all costs and expenses of maintaining such suit or action,
including reasonable attorneys' fees.

         3.12 ENTIRE AGREEMENT. Except as otherwise expressly set forth herein,
this document embodies the complete agreement and understanding among the
parties hereto with respect to the subject matter hereof and supersedes and
preempts any prior understandings, agreements or representation by or among the
parties, written or oral, which may have related to the subject matter hereof in
any way.

         3.13 NOTICE. Any notice provided for in this Agreement must be in
writing and must be either personally delivered or mailed first class to the
recipient at the address indicated by the Company's records, or at such address
or the attention of such other person as the recipient party has specified by
prior written notice to the sending party.

         3.14 RELIANCE. The Stockholders may rely upon written notice from the
group or entity named in subsection 1.2 with respect to the identity of the
person designated by such entity or group to serve on the Board pursuant to
subsection 1.2. Each entity or group entitled to designate a director agrees to
provide such notice in good faith immediately upon request.

         3.15 COUNTERPARTS. This Agreement may be executed in one or more
counterparts, each of which will be deemed an original but all of which together
shall constitute one and the same agreement.

              [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                       7
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this THIRD AMENDED
AND RESTATED STOCKHOLDERS AGREEMENT as of the date first above written.

COMPANY:                                      INVESTORS:

MYOGEN, INC.                                  SEQUEL LIMITED PARTNERSHIP

                                              By: Sequel Venture Partners, LLC
By: /s/ J. William Freytag                        its General Partner
    -------------------------------------
    J. William Freytag
    President and Chief Executive Officer     By: /s/ Dan Mitchell
                                                  ------------------------------
                                                  General Partner

KEY STOCKHOLDERS:                             SEQUEL EURO LIMITED PARTNERSHIP

                                              By: Sequel Venture Partners, LLC
/s/ Michael R. Bristow                            its General Partner
-----------------------------------------
Michael R. Bristow

SAVACOR TRUST                                 By: /s/ Dan Mitchell
                                                  ------------------------------
                                                  Manager

By: /s/ Michael R. Bristow                    CROSSPOINT VENTURE PARTNERS 1997
-----------------------------------------

INVESTOCOR TRUST
                                              By: /s/ Don Milder
                                                  ------------------------------
                                                  General Partner
By: /s/ Michael R. Bristow
-----------------------------------------

                                              INTERWEST PARTNERS VI, LP
/s/ Michael Juliano
-----------------------------------------     By: /s/ Arnold Oronsky
Michael Juliano                                   ------------------------------
                                                  General Partner

/s/ Leslie A. Leinwand
-----------------------------------------
Leslie A. Leinwand

                                              INTERWEST INVESTORS VI, LP
/s/ M. Benjamin Perryman
-----------------------------------------
M. Benjamin Perryman                          By: /s/ Arnold Oronsky
                                                  ------------------------------
                                                  General Partner

/s/ Milton Levin
-----------------------------------------
Milton Levin

/s/ Frank Stewart
-----------------------------------------
Frank Stewart

                             STOCKHOLDERS AGREEMENT

<PAGE>

/s/ J. William Freytag
-----------------------------------------
J. William Freytag

                                              NEW ENTERPRISE ASSOCIATES 9,
                                              LIMITED PARTNERSHIP

/s/ Joseph L. Turner
-----------------------------------------
Joseph L. Turner                              By: NEA Partners 9, Limited
                                                  Partnership

By:                                           /s/ C. Richard Kramlich
                                              ----------------------------------
/s/ John R. Julian                            C. Richard Kramlich
-----------------------------------------     General Partner
John R. Julian

                                              NEA PRESIDENTS FUND, L.P.

/s/ Ellen Leigh Curtin
-----------------------------------------
Ellen Leigh Curtin                            By: NEA General Partners, L.P.

                                              By: /s/ C. Richard Kramlich
                                              ----------------------------------
                                              General Partner -
                                              C. Richard Kramlich
/s/ Richard J. Gorczynski
-----------------------------------------
Richard J. Gorczynski

                                              NEA VENTURES 1999, LIMITED
                                              PARTNERSHIP
/s/ Gordon Van Dusen
-----------------------------------------
Gordon Van Dusen                              By: /s/ Jacqueline Myers
                                                  ------------------------------
                                                  Vice President -
                                                  Jacqueline Myers

/s/ Eric N. Olson                             NEW VENTURE PARTNERS IV L.P.
-----------------------------------------
Eric N. Olson
                                              By: /s/
                                                  ------------------------------

                                              By: /s/
                                                  ------------------------------

                                              CMEA LIFE SCIENCES FUND, L.P.

                                              By: /s/ Thomas R. Baruch
                                                  ------------------------------
                                                  General Partner

                             STOCKHOLDERS AGREEMENT

<PAGE>

                                              J.P. MORGAN PARTNERS (SBIC), LLC

                                              By: /s/ Rodney A. Ferguson
                                                  ------------------------------

                                              Its: Managing Director
                                                   -----------------------------

                                              NEW ENTERPRISE ASSOCIATES 10,
                                              LIMITED PARTNERSHIP

                                              By: NEA Partners 10, Limited
                                                  Partnership

                                              By: /s/ C. Richard Kramlich
                                                  ------------------------------
                                                  C. Richard Kramlich -
                                                  General Partner

                                              J.P. MORGAN SECURITIES INC.

                                              By: /s/ James F. Zanze
                                                  ------------------------------

                                              Its: Managing Director
                                                   -----------------------------

                                              BVCF IV, L.P.

                                              By: J.W. Puth Associates, LLC,
                                                  its General Partner

                                              By: Brinson Venture Management,
                                                  LLC, its Attorney-in-fact

                                              By: Adams Street Partners, LLC,
                                                  as its Administrative Member

                                              By: /s/ Terry Gould
                                                  ------------------------------
                                                  Terry Gould
                                                  Partner

                                              INTERWEST PARTNERS VIII, LP

                                              By: InterWest Management Partners
                                                  VIII, LLC, its general partner

                                              By: /s/ Arnold Oronsky
                                                  ------------------------------

                             STOCKHOLDERS AGREEMENT

<PAGE>

                                              INTERWEST INVESTORS VIII, LP

                                              By: InterWest Management Partners
                                                  VIII, LLC, its general partner

                                              By: /s/ Arnold Oronsky
                                                  ------------------------------

                                              INTERWEST INVESTORS Q VIII, LP

                                              By: InterWest Management Partners
                                                  VIII, LLC, its general partner

                                              By: /s/ Arnold Oronsky
                                                  ------------------------------

                                              PACIFIC RIM LIFE SCIENCE NO. 1
                                              INVESTMENT PARTNERSHIP

                                              By: Pacific Rim Life Science
                                                  No. 1/2 Investment
                                                  Partnership, its general
                                                  partner

                                              By: /s/ Masahiro Michishita
                                                  ------------------------------
                                                  Masahiro Michishita, M.D.,
                                                  Ph.D., Managing General
                                                  Partner

                                              PACIFIC RIM LIFE SCIENCE NO. 2
                                              INVESTMENT PARTNERSHIP

                                              By: Pacific Rim Life Science
                                                  No. 1/2 Investment
                                                  Partnership, its general
                                                  partner

                                              By: /s/ Masahiro Michishita
                                                  ------------------------------
                                                  Masahiro Michishita, M.D.,
                                                  Ph.D., Managing General
                                                  Partner

                                              HFM CHARITABLE REMAINDER TRUST

                                              By: /s/ Roy M. Jones
                                                  ------------------------------
                                                  Roy M. Jones, Authorized Agent

                             STOCKHOLDERS AGREEMENT

<PAGE>

                                              MONTAGU NEWHALL GLOBAL PARTNERS LP

                                              By: /s/ C. Ashton Newhall
                                                  ------------------------------

                                              Name: Ashton Newhall
                                                    ----------------------------

                                              Title: General Partner
                                                     ---------------------------

                                              /s/ David N. Low, Jr.
                                              ----------------------------------
                                              David N. Low, Jr.

                                              /s/ Jim F. Zanze
                                              ----------------------------------
                                              Jim F. Zanze

                                              /s/ Philippe McAuliffe
                                              ----------------------------------
                                              Philippe McAuliffe

                                              /s/ Mike Gaito
                                              ----------------------------------
                                              Mike Gaito

                             STOCKHOLDERS AGREEMENT

<PAGE>

                                              CHINA DEVELOPMENT INDUSTRIAL
                                              BANK INC.

                                              By: CHINA DEVELOPMENT INDUSTRIAL
                                                  BANK INC.

                                              By: /s/ Tai-ying Liu
                                                  ------------------------------
                                                  Tai-ying Liu, Chairman & CEO

                             STOCKHOLDERS AGREEMENT

<PAGE>

                                              PERSEUS-SOROS BIOPHARMACEUTICAL
                                              FUND, LP

                                              By: Perseus-Soros Partners, LLC,
                                                  General Partner

                                                  By: SFM Participation, LP,
                                                      Member

                                                  By: SFM AH, Inc., General
                                                      Partner

                                                  /s/ Richard D. Holahan, Jr.
                                                  ------------------------------
                                                  By: Richard D. Holahan, Jr.
                                                  Title: Secretary

                             STOCKHOLDERS AGREEMENT

<PAGE>

                                              HUNT VENTURES, L.P.

                                              By: /s/ J. Fulton Murray III
                                                  ------------------------------

                                              Name: J. Fulton Murray, III
                                                    ----------------------------

                                              Title: Managing Director

                                              SILICON VALLEY BANCVENTURES, L.P.

                                              By: Silicon Valley BancVentures,
                                                  Inc., Its General Partner

                                              By: /s/ Greg Becker
                                                  ------------------------------
                                              Name: Greg Becker
                                                    ----------------------------
                                              Title: Investment Manager
                                                     ---------------------------

                             STOCKHOLDERS AGREEMENT

<PAGE>

                                              Pacific Rim Capital LLC

                                              /s/ T. Chester Wang
                                              ----------------------------------
                                              T. Chester Wang, Manager

                                              /s/ James Margolis, MD
                                              ----------------------------------
                                              James Margolis, MD

                                              THOMAS J. TOY & CONSTANCE K. TOY,
                                              JTWROS

                                              /s/ Thomas J. Toy
                                              ----------------------------------
                                              Thomas J. Toy

                                              /s/ Constance K. Toy
                                              ----------------------------------
                                              Constance K. Toy

                                              /s/ Walter M. Narajowski
                                              ----------------------------------
                                              Walter M. Narajowski

                                              DIECK-MCGURK AND ASSOCIATES, LP

                                              By: /s/ Ronald Dieck
                                              ----------------------------------
                                              Ronald Dieck, General Partner

                                              /s/ Daniel Ruben
                                              ----------------------------------
                                              Daniel Ruben

                                              /s/ David Pflueger
                                              ----------------------------------
                                              David Pflueger

                                              /s/ James Larrick
                                              ----------------------------------
                                              James Larrick

                             STOCKHOLDERS AGREEMENT

<PAGE>

                                    EXHIBIT A

                            LIST OF KEY STOCKHOLDERS

Michael R. Bristow

Savacor Trust

InvestoCor Trust

Michael Juliano

Milton Levin

Leslie A. Leinward

M. Benjamin Perryman

Frank Stewart

J. William Freytag

Joseph L. Turner

John R. Julian

Ellen Leigh Curtin

Richard J. Gorczynski

Gordon Van Dusen

Eric N. Olson

<PAGE>

                                    EXHIBIT B

                                LIST OF INVESTORS

Sequel Limited Partnership
4430 Arapahoe Avenue, Suite 220
Boulder, CO 80303

Sequel Euro Limited Partnership
4430 Arapahoe Avenue, Suite 220
Boulder, CO 80303

Crosspoint Venture Partners 1997
18552 MacArthur Blvd., Suite 400
Irvine, CA 92612

InterWest Partners VI, L.P.
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA 94025

InterWest Investors VI, L.P.
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA 94025

New Enterprise Associates 9, Limited Partnership
1119 St. Paul Street
Baltimore, MD 21202
Attn: Gene Trainor

NEA Presidents Fund, L.P.
1119 St. Paul Street
Baltimore, MD 21202
Attn: Gene Trainor

NEA Ventures 1999, Limited Partnership
1119 St. Paul Street
Baltimore, MD 21202
Attn: Gene Trainor

New Venture Partners IV L.P.
1119 St. Paul Street
Baltimore, MD 21202

CMEA Life Sciences Fund, L.P.
One Embarcadero Center, Suite 3250
San Francisco, CA  94111
Attn: Meryl L. Schreibstein

<PAGE>

J.P. Morgan Partners (SBIC), LLC
50 California Street, Suite 2940
San Francisco, CA 94111
Attn: Rod Ferguson

With a copy to:

J.P. Morgan Partners
Official Notices Clerk
1221 Avenue of the Americas
New York, NY 10020
Facsimile: (212) 899-3401

and

J.P. Morgan Partners (SBIC), LLC
50 California Street, Suite 2940
San Francisco, CA 94111
Attn: Shannon Horton

New Enterprise Associates 10, Limited Partnership
1119 St. Paul Street
Baltimore, MD 21202
Attn: Gene Trainor

J.P. Morgan Securities Inc.
c/o Kathy Choi
225 Bush St., 4th Floor
San Francisco, CA 94104

BVCF IV, L.P.
c/o Adams Street Partners, LLC
209 South LaSalle Street
Chicago, IL 60604
Attn: Craig S. Taylor, Ph.D.

InterWest Partners VIII, L.P.
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA 94025
Attn: Arnold L. Oronsky

InterWest Investors VIII, L.P.
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA 94025
Attn: Arnold L. Oronsky

                                       2
<PAGE>

InterWest Investors Q VIII, L.P.
3000 Sand Hill Road
Building 3, Suite 255
Menlo Park, CA 94025
Attn: Arnold L. Oronsky

Pacific Rim Life Science No.1 Investment Partnership
(C/O) Pacific Rim Ventures Co., Ltd.
2nd Floor, Green Plaza
3-7-20 Komazawa, Setagaya-ku
Tokyo 154-0012, Japan

Pacific Rim Life Science No.2 Investment Partnership
(C/O) Pacific Rim Ventures Co., Ltd.
2nd Floor, Green Plaza
3-7-20 Komazawa, Setagaya-ku
Tokyo 154-0012, Japan

Both care of:
Daisuke Takahashi, Vice President, Pacific Rim Ventures Co., Ltd.
2nd Floor, Green Plaza
3-7-20 Komazawa, Setagaya-ku
Tokyo 154-0012, Japan
TEL: 81-3-5779-6752
FAX: 81-3-5779-6753
dta@pacificrim-ventures.com

HFM Charitable Remainder Trust
3060 Peachtree Road NW
Nineteenth Floor
Atlanta, GA  30305
Attn: Roy M. Jones

Montagu Newhall Global Partners LP
52 Upper Brook Street
London W1K 2BU
Attention: Rupert Montagu

David N. Low, Jr
21 Deer Park Drive
Greenwich, CT 06831

Jim Zanze
2371 Broadway
San Francisco, CA. 94115

Philippe McAuliffe
19 East 7th St., Apt. 4
New York, NY 10003

                                       3
<PAGE>

Mike Gaito
95 Horatio Street, Apt. 4C
New York, NY 10014

China Development Industrial Bank Inc.
125 Naking East Road Section 5
Overseas Business Department
Taipei, 105
Taiwan
Attn: Claire Tsai, Assistant Manager

Perseus-Soros Biopharmaceutical Fund, LP
888 Seventh Avenue, 29th Floor
New York, NY  10106
Attn: Steve Elms
      Andrew N. Schiff

with a copy to:

Perseus-Soros Biopharmaceutical Fund, L.P.
c/o Soros Fund Management LLC
888 Seventh Avenue, 31st Floor
New York, NY 10106
Attention: Richard D. Holahan, Jr., Esq.

and

Paul, Weiss, Rifkind, Wharton & Garrison
1285 Avenue of the Americas
New York, New York 10019-6064
Attention: Bruce A. Gutenplan, Esq.

Hunt Ventures, L.P.
Suite 1500
1445 Ross Avenue
Dallas, TX  75202
Attn: Fulton Murray
      Tom Hurtekant, Esq.

Silicon Valley BancVentures L.P.
c/o
Silicon Valley BancVentures, Inc.
Attn: Greg Becker
3000 Sand Hill Road
Building 1, Suite 200
Menlo Park, CA 94025

                                       4
<PAGE>

T. Chester Wang
c/o Acorn Campus LLC
6 Results Way
Cupertino, CA 95014

James Margolis, MD
4701 Meridian Avenue
Suite 440, Adams Building
Miami Beach, FLA 33140

Thomas J. Toy & Constance K. Toy, JTWROS
331 Parrott Drive
San Mateo, CA 94402

Walter M. Narajowski
84 Blue Lagoon
Laguna Beach, Ca. 92651

Dieck-McGurk and Associates, LP
335 Lowell Avenue
Palo Alto, CA  94301
Attn: Ron Dieck and Erin McGurk

Daniel Ruben
15233 Camarillo St.
Sherman Oaks, CA 91403

David Pflueger
Pluris Healthcare Systems
16596 W. Bayaud Dr.
Golden, CO 80401

James Larrick
Panorama Research
2462 Wyandotte
Mt. View, CA 94043

                                       5
<PAGE>

                                  MYOGEN, INC.

                             FIRST AMENDMENT TO THE
                THIRD AMENDED AND RESTATED STOCKHOLDERS AGREEMENT

         Pursuant to Section 3.6 of the Third Amended and Restated Stockholders
Agreement, by and among Myogen, Inc. (the "Company") and the Investors and Key
Stockholders named therein, dated as of August 21, 2001 (the "Agreement"), the
Company and each of the undersigned Investors and Key Stockholders hereby agree,
effective as of this 20th day of December, 2001 to the amendment (the
"Amendment") set forth below. Capitalized terms used but not defined herein have
the meanings given them in the Agreement.

                                    RECITALS

         A. In connection with the sale and issuance of additional shares of its
Series D Preferred Stock pursuant to that certain Series D Preferred Stock
Purchase Agreement, dated August 21, 2001, as amended on November 2, 2001, the
Company wishes amend Section 1.2 (ii)(4) of the Agreement to provide that
representative of Perseus Soros as a Series D Designee to its Board of
Directors.

                                    AGREEMENT

            The parties to the Agreement hereby agree as follows:

         1. Section 1.2(ii)(4) of the Agreement is hereby amended and restated
to read in its entirety as set forth below:

                  "(4) three (3) people (each a "SERIES D DESIGNEE") designated
         by the Stockholders holding a majority of the Series D Stock, one of
         whom shall be nominated by J.P. Morgan Partners (SBIC), LLC or its
         affiliates (the "J.P. MORGAN NOMINEE"), one of whom shall be nominated
         by Perseus Soros (the "PERSEUS SOROS NOMINEE") and one of whom shall be
         an experienced pharmaceutical executive. The J.P. Morgan Nominee shall
         initially be Rodney Ferguson, the Perseus Soros Nominee shall initially
         be Andrew N. Schiff, M.D. and the other Series D Designee shall be
         selected after the date of the Financing."

         2. This Amendment may be executed in any number of counterparts, each
of which may be executed by less than all of the parties hereto and each of
which shall constitute one and the same instrument.

         3. The undersigned Purchasers consent to a restatement of the Agreement
to incorporate this Amendment.

         4. This Amendment shall be effective upon its execution by the Company
and the holders of sixty-five percent (65%) in interest of the Investors and a
majority in interest of the Key Stockholders.

         5. The Amendment shall be governed and construed in accordance with the
laws of the State of Colorado as though made solely among residents of the State
of Colorado without regard to conflicts of law principals.

                                       1
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this First
Amendment to the Third Amended and Restated Stockholders Agreement as of the
date set forth in the first paragraph above.

COMPANY:                                      INVESTORS:

MYOGEN, INC.                                  SEQUEL LIMITED PARTNERSHIP

                                              By: Sequel Venture Partners, LLC
By: /s/ J. William Freytag                        its General Partner
    -------------------------------------
    J. William Freytag
    President and Chief Executive Officer     By: /s/ Dan Mitchell
                                                  ------------------------------
                                                  General Partner

KEY STOCKHOLDERS:                             SEQUEL EURO LIMITED PARTNERSHIP

                                              By: Sequel Venture Partners, LLC
/s/ Michael R. Bristow                            its General Partner
----------------------------------------
Michael R. Bristow

SAVACOR TRUST                                 By: /s/ Dan Mitchell
                                                  ------------------------------
                                                  Manager

By: Michael R. Bristow                        CROSSPOINT VENTURE PARTNERS 1997
    ------------------------------------

INVESTOCOR TRUST
                                              By: /s/ Don Milder
                                                  ------------------------------
                                                  General Partner
By: Michael R. Bristow
    ------------------------------------

                                              INTERWEST PARTNERS VI, LP
/s/ Michael Juliano
---------------------------------------
Michael Juliano                               By: /s/ Arnold Oronsky
                                                  ------------------------------
                                                  General Partner

/s/ Leslie A. Leinwand
---------------------------------------
Leslie A. Leinwand

/s/ M. Benjamin Perryman                      INTERWEST INVESTORS VI, LP
---------------------------------------
M. Benjamin Perryman
                                              By: /s/ Arnold Oronsky
                                                  ------------------------------
                                                  General Partner
/s/
---------------------------------------
Milton Levin

/s/ Frank Stewart
---------------------------------------
Frank Stewart

                       FIRST AMENDMENT TO THE MYOGEN, INC.
                THIRD AMENDED AND RESTATED STOCKHOLDERS AGREEMENT

<PAGE>

/s/ J. William Freytag
---------------------------------------
J. William Freytag

                                              NEW ENTERPRISE ASSOCIATES 9,
                                              LIMITED PARTNERSHIP
/s/ Joseph L. Turner
---------------------------------------
Joseph L. Turner                              By: NEA Partners 9, Limited
                                                  Partnership

                                              By: /s/ C. Richard Kramlich
                                                  ------------------------------
/s/ John R. Julian                                C. Richard Kramlich
---------------------------------------           General Partner
John R. Julian

                                              NEA PRESIDENTS FUND, L.P.

/s/ Ellen Leigh Curtin
---------------------------------------
Ellen Leigh Curtin                            By: NEA General Partners, L.P.

                                              By: /s/ C. Richard Kramlich
                                                  ------------------------------
                                                  General Partner -
                                                  C. Richard Kramlich
/s/ Richard J. Gorczynski
---------------------------------------
Richard J. Gorczynski
                                              NEA VENTURES 1999, LIMITED
                                              PARTNERSHIP
/s/ Gordon Van Dusen
---------------------------------------
Gordon Van Dusen                              By: /s/ Jacqueline Myers
                                                  ------------------------------
                                                  Vice President -
                                                  Jacqueline Myers

                                              NEW VENTURE PARTNERS IV L.P.
/s/ Eric N. Olson
---------------------------------------
Eric N. Olson                                 By:
                                                  ------------------------------

                                              By:
                                                  ------------------------------

                                              CMEA LIFE SCIENCES FUND, L.P.

                                              By: /s/ Thomas R. Baruch
                                                  ------------------------------
                                                  General Partner

                       FIRST AMENDMENT TO THE MYOGEN, INC.
                THIRD AMENDED AND RESTATED STOCKHOLDERS AGREEMENT

                                       2
<PAGE>

                                                  J.P. MORGAN PARTNERS (SBIC),
                                                  LLC

                                                  By: /s/ Rodney A. Ferguson
                                                      -------------------------

                                                  Its: Managing Director
                                                       -------------------------

                                                  NEW ENTERPRISE ASSOCIATES 10,
                                                  LIMITED PARTNERSHIP

                                                  By: NEA Partners 10, Limited
                                                      Partnership

                                                  By: /s/ C. Richard Kramlich,
                                                      --------------------------
                                                  C. Richard Kramlich, General
                                                  Partner

                                                  J.P. MORGAN SECURITIES INC.

                                                  By: /s/ James F. Zanze
                                                      --------------------------

                                                  Its: Managing Director
                                                       -------------------------

                                                  BVCF IV, L.P.

                                                  By: J.W. Puth Associates, LLC,
                                                      its General Partner

                                                  By: Brinson Venture
                                                      Management, LLC, its
                                                      Attorney-in-fact

                                                  By: Adams Street Partners,
                                                      LLC, as its Administrative
                                                      Member

                                                  By: /s/ Craig S. Taylor
                                                      --------------------------
                                                      Craig S. Taylor
                                                      Partner

                                                  INTERWEST PARTNERS VIII, LP

                                                  By: InterWest Management
                                                      Partners VIII, LLC, its
                                                      general partner

                                                  By: /s/ Arnold Oronsky
                                                      --------------------------

                                                  INTERWEST INVESTORS VIII, LP

                                                  By: InterWest Management
                                                      Partners VIII, LLC, its
                                                      general partner

                                                  By: /s/ Arnold Oronsky
                                                      --------------------------

                       FIRST AMENDMENT TO THE MYOGEN, INC.
                THIRD AMENDED AND RESTATED STOCKHOLDERS AGREEMENT

                                       3
<PAGE>

                                              INTERWEST INVESTORS Q VIII, LP

                                              By: InterWest Management
                                                  Partners VIII, LLC, its
                                                  general partner

                                              By:
                                                  ------------------------------

                                              PACIFIC RIM LIFE SCIENCE NO. 1
                                              INVESTMENT PARTNERSHIP

                                              By: Pacific Rim Life Science
                                                  No. 1/2 Investment
                                                  Partnership, its general
                                                  partner

                                              By: /s/ Masahiro Michishita
                                                  ------------------------------
                                                  Masahiro Michishita, M.D.,
                                                  Ph.D., Managing General
                                                  Partner

                                              PACIFIC RIM LIFE SCIENCE NO. 2
                                              INVESTMENT PARTNERSHIP

                                              By: Pacific Rim Life Science
                                                  No. 1/2 Investment
                                                  Partnership, its general
                                                  partner

                                              By: /s/ Masahiro Michishita
                                                  ------------------------------
                                                  Masahiro Michishita, M.D.,
                                                  Ph.D., Managing General
                                                  Partner

                                              HFM CHARITABLE REMAINDER TRUST

                                              By:
                                                  ------------------------------
                                                  Roy M. Jones, Authorized Agent

                       FIRST AMENDMENT TO THE MYOGEN, INC.
                THIRD AMENDED AND RESTATED STOCKHOLDERS AGREEMENT

                                       4
<PAGE>

                                              MONTAGU NEWHALL GLOBAL PARTNERS LP

                                              By: /s/ C. Ashton Newhall
                                                  ------------------------------

                                              Name: C. Ashton Newhall
                                                    ----------------------------

                                              Title: General Partner
                                                     ---------------------------

                                              ----------------------------------
                                              David N. Low, Jr.

                                              /s/ Jim F. Zanze
                                              ----------------------------------
                                              Jim F. Zanze

                                              ----------------------------------
                                              Philippe McAuliffe

                                              ----------------------------------
                                              Mike Gaito

                                              CHINA DEVELOPMENT INDUSTRIAL
                                              BANK INC.

                                              By:
                                                  ------------------------------
                                              Name:
                                                    ----------------------------
                                              Title:
                                                     ---------------------------

                       FIRST AMENDMENT TO THE MYOGEN, INC.
                THIRD AMENDED AND RESTATED STOCKHOLDERS AGREEMENT

                                       5

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00055-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00055-of-00352.parquet"}]]