Document:

<PAGE>
                                                                   EXHIBIT 10.28

                            FIRST AMENDMENT TO LEASE

         This First Amendment to Lease Agreement ("First Amendment") is to be
effective December 2, 2003 ("Effective Date"), by and between Sevo Miller, Inc.,
as receiver ("Receiver") on behalf of Church Ranch Business Center, LLC, by that
certain Order Appointing Receiver dated June 16, 2003, and Myogen, Inc.,
("Tenant"). The Tenant and Receiver may be referred to herein as the "Parties"
and either one of them may be referred to herein as a "Party."

                                    RECITALS

         A. Church Ranch Business Center, LLC, a Colorado limited liability
company, as landlord ("Landlord") and Tenant entered into that certain Lease
Agreement dated January 1, 2002 (the "Lease"), for the lease of space designated
as Suites 102-107, Building l, and Suites 209-212, Building 2, totaling
approximately 22,040 gross square feet, in the Church Ranch Business Center,
7575-7577 West 103rd Avenue, Westminster, Colorado, 80021 (the "Project").

         B. The Tenant has requested the Receiver to enter into a lease for an
additional 6,202 square feet of adjacent space known as Suite 213, Building 2
("Additional Space") at the Project, and Tenant and Receiver have agreed to
amend the terms of the Lease to permit Tenant to lease the Additional Space.

         In consideration of the mutual agreements set forth herein, the
Receiver and Tenant agree that the Lease will be amended as follows:

         1. Property. As of the Effective Date hereof, the definition of the
"Property," as defined in Section 1.04 of the Lease is amended to include the
Additional Space. The Additional Space is depicted on Exhibit A to this First
Amendment. Except as set forth herein, the Property shall be deemed to include
the Additional Space for all purposes under the Lease.

         2. Term. The definition of "Lease Term" as set forth in Section 1.05
shall be applicable to the Additional Space and, therefore, shall end on
February 28, 2007. Notwithstanding the foregoing, Landlord and Tenant
acknowledge and agree that Tenant's rights pursuant to Section 5 of Exhibit A to
the Lease shall apply to the Additional Space.

         3. Base Rent. The Base Rent as described in Section 1.12(a) of the
Lease, for the Additional Space shall be the fixed amount of $4,393.00 per month
(based upon a rate of $8.50 per foot times 6,202 square feet). Tenant's
obligation to pay Base Rent for the Additional Space shall commence on the
earlier to occur of (i) the date that Tenant begins transacting business in the
Additional Space after having substantially completed its build out of the
Additional Space, or (ii) April 1, 2004, and shall continue through the end of
the Lease Term. The initial Base Rent payment for the Additional Space shall be
due and payable on or before the commencement of Tenant's obligation to pay Base
Rent for the Additional Space.

         4. Other Periodic Payments. As of the Effective Date hereof, Tenant's
pro rata share as calculated in Section 4.05(e) of the Lease and as set forth in
Section 12(b) of the Lease shall be increased to 22.32% (= (22,040 +
6,202)/126,550).

                                     Page 1
<PAGE>

         5. Acceptance of Additional Space. The taking of possession of the
Additional Space shall be deemed an acceptance of the same by Tenant in its "AS
IS" condition without any obligation whatsoever on the part of the Receiver or
Landlord to repair, remodel, reconstruct or modify the Additional Space for
Tenant. THERE ARE NO IMPLIED WARRANTIES OF MERCHANTABILITY, HABITABILITY OR
FITNESS FOR A PARTICULAR PURPOSE WITH RESPECT TO THE ADDITIONAL SPACE, OR OF ANY
OTHER HIND ARISING OUT OF THIS FIRST AMENDMENT, AND THERE ARE NO WARRANTIES WITH
RESPECT TO THE ADDITIONAL SPACE THAT EXTEND BEYOND THOSE EXPRESSLY STATED IN
THIS FIRST AMENDMENT.

         6. Use and Rights. Landlord and Tenant acknowledge and agree that (i)
Tenant shall be entitled to operate in the Additional Space in the same manner
as is permitted for all or any portion of the original Property under the Lease,
and (ii) any and all rights that Tenant has with respect to all or any portion
of the original Property shall apply to the Additional Space. Notwithstanding
the foregoing or any other provision of the Lease, Tenant will not be required
to remove the tenant improvements which Tenant installs or constructs in the
Premises, provided that Tenant shall be required to remove all of Tenant's
equipment, supplies, furniture, hazardous materials, inventory, appliances and
other easily movable property, and leave the premises in a "broom clean
condition."

         7. Condition Precedent. Notwithstanding anything to the contrary
contained herein, the effectiveness of this First Amendment is contingent upon
obtaining the consent of the court having jurisdiction over the receivership of
the Property on or before December l, 2003.

         8. Counterparts. This First Amendment may be executed in counterparts
and the parties agree that facsimile signatures shall be sufficient to bind the
parties to the terms hereof.

         9. Definitions and Ratification. Tenant acknowledges that neither
Landlord nor the Receiver are in default under any term or provision set forth
in the Lease as of the date of this First Amendment. Capitalized terms in this
First Amendment which are not expressly defined herein shall have the meanings
set forth in the Lease. Except as amended by this First Amendment, the Lease is
hereby ratified and confirmed.

                                     Page 2
<PAGE>

         The Landlord and Tenant have signed this First Amendment to be
effective the date first set forth above.

                                    RECEIVER:

                                    SEVO MILLER, INC.

                                    By: /s/ John M. Sevo
                                        ----------------------------------------
                                            John M. Sevo, CEO

                                    TENANT:

                                    MYOGEN, INC.

                                    By: /s/ J. William Freytag
                                        ----------------------------------------
                                    Name: J. William Freytag, PhD
                                          --------------------------------------
                                    Title: President + CEO
                                           -------------------------------------

                                     Page 3<PAGE>
                                                                   EXHIBIT 10.29

                              [/\#/\] CERTAIN CONFIDENTIAL INFORMATION CONTAINED
                                  IN THIS DOCUMENT, MARKED BY BRACKETS, HAS BEEN
                                OMITTED AND FILED SEPARATELY WITH THE SECURITIES
                                  AND EXCHANGE COMMISSION PURSUANT TO RULE 24B-2
                             OF THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.

                               THIRD AMENDMENT TO
                     INTELLECTUAL PROPERTY LICENSE AGREEMENT

         THIS THIRD AMENDMENT TO INTELLECTUAL PROPERTY LICENSE AGREEMENT
("AMENDMENT") is entered into as of November 24, 2003 ("THIRD AMENDMENT DATE")
by and between UNIVERSITY LICENSE EQUITY HOLDINGS, INC. ("ULEHI") and MYOGEN,
INC. ("MYOGEN"), a Delaware corporation, having its principal place of business
at 7575 W. 103rd Avenue, Westminster, Colorado 80021.

         WHEREAS, ULEHI (as successor-in-interest to University Technology
Corporation) and Myogen are parties to that certain Intellectual Property
License Agreement dated September 1, 1998, as amended January 26, 2001 and
November 12, 2002 (the "LICENSE AGREEMENT"), pursuant to which ULEHI licensed
certain intellectual property on an exclusive basis to Myogen in exchange for
the right to receive certain payments;

         WHEREAS, ULEHI and Myogen now desire to amend the License Agreement to
restate the intellectual property to which the exclusive license extends and to
reflect the parties' agreement regarding the modification of certain of such
payment terms, and

         NOW, THEREFORE, in consideration of the foregoing premises and the
covenants contained herein, ULEHI and Myogen agree to amend the License
Agreement as follows:

1. All capitalized terms used but not defined herein have the meaning given them
in the License Agreement.

2. SECTION 1.3 is deleted in its entirety and replaced with the following:

         1.3      A "Licensed Product" shall mean any product or substantial
                  part thereof which:

                  (a)      is based on the Intellectual Property and/or which is
                           covered in whole or in part by an issued, unexpired
                           claim or a pending claim contained in the
                           Intellectual Property and Know How in the country in
                           which the Licensed Product is made, used or sold;

                  (b)      is manufactured using a Licensed Process;

                  (c)      is derived from Intellectual Property and/or
                           Know-How.

                  Except as otherwise indicated in this Agreement, License
                  Product shall include enoximone if and only if the enoximone
                  is sold after U.S. FDA approval and only in combination (i.e.,
                  orally administered with beta blockers) therapy as described
                  in the relevant patent filed by the University of Colorado.

3.       SECTION 3.2(c) is deleted in its entirety and replaced with the
         following:

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED

                                       1.
<PAGE>

         (c)      LICENSEE together with its sublicensees, shall have sold a
                  minimum number of products containing enoximone (alone or in
                  combination) with annual sales that exceed the amounts in the
                  following schedule:

                  [/\#/\]                  [/\#/\]
                  [/\#/\]                  [/\#/\]
                  [/\#/\]                  [/\#/\]
                  [/\#/\]                  [/\#/\]

                  * and each year of the Agreement thereafter.

4. SECTION 3.3 is deleted in its entirety and replaced with the following:

         3.3 If LICENSEE fails to perform in accordance with Paragraphs 3.1 and
3.2 above, LICENSEE shall have the right to make royalty payments to ULEHI based
on the Net Sales amounts indicated above. If LICENSEE does not pay such amounts,
ULEHI may reduce the exclusive license under this Agreement to a nonexclusive
one, provided however, that LICENSEE achieves at least [/\#/\] of the Net Sales
stated in Paragraph 3.2. If LICENSEE does not pay such amount and does not
achieve at least [/\#/\] of the Net Sales stated in Paragraph 3.2, then ULEHI
may terminate this Agreement pursuant to Paragraph 13.3 hereof unless both
parties renegotiate the Due Diligence plan and mutually agree to revisions
thereto.

5. SECTION 4.1(c) is deleted in its entirety and replaced with the following:

         (c)      RUNNING ROYALTIES AS FOLLOWS:

                  (i)      [/\#/\] of Net Sales (other than to sublicensees) of
                           the Licensed Products by LICENSEE.

                  (ii)     [/\#/\] of the amount of royalty payments received by
                           LICENSEE from such Net Sales by sublicensees;
                           provided, that in no event will this amount exceed
                           [/\#/\] of sublicensee's Net Sales.

                  In the event of extenuating circumstances, royalty rates for
         any given technology will be renegotiated in good faith.

6. SECTION 4.1(d) is deleted in its entirety and replaced with the following:

         (d)      In addition to the foregoing, LICENSEE agrees that it will
                  remit to ULEHI [/\#/\] of any Option Fee, License Fee, or any
                  other front-end payment (excluding any payment received for
                  reimbursement of R&D, Clinical Studies, FDA requirements,
                  loans or stocks sales) which it may receive from any
                  sublicensee in relation to Licensed Products and/or Licensed
                  Processes and/or Know-How; provided, however, if LICENSEE
                  receives any such payment from a sublicensee in relation to
                  Licensed Products and/or Licensed Processes and/or Know-How
                  and such payment is also in consideration for the grant of a
                  license or sublicense to other technology controlled by
                  LICENSEE but not acquired from ULEHI hereunder, then the
                  foregoing amount shall be adjusted by a percentage that fairly

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED

                                       2.
<PAGE>

                  represents the contribution of the relevant Intellectual
                  Property and/or Know-How to the total payment received by
                  LICENSEE.

7. The following provision shall be added as SECTION 4.1(f):

         (f) LICENSEE shall make the following non-refundable milestone payments
to ULEHI within thirty (30) days of the occurrence of the following development
events, on a per Licensed Product (excluding, for this purpose, enoximone, alone
or in combination) basis:

<Table>
<Caption>
         Development Milestone                                                       Payment
         ---------------------                                                       -------
<S>                                                                                <C>
         [/\#/\]                                                                     [/\#/\]
         [/\#/\]                                                                     [/\#/\]
         [/\#/\]                                                                     [/\#/\]
</Table>

         Each milestone payment shall be paid only once per Licensed Product,
and the total amount of milestone payments to be paid by LICENSEE for each
Licensed Product shall not exceed [/\#/\].

8. ARTICLE V of the License Agreement shall be deleted in its entirety and
replaced with the following:

                               ARTICLE V - OPTIONS

         5.1 At LICENSEE's discretion, LICENSEE shall provide to ULEHI minimum
annual research support payments equal to [/\#/\] per year in order to secure
the exclusive option described in Paragraph 5.2 below.

         5.2 ULEHI hereby grants to LICENSEE an exclusive option to any
inventions in the Field conceived or reduced to practice by Dr. Michael Bristow,
Dr. Leslie Leinwand and/or Dr. Ben Perryman and their University of Colorado
collaborators (as defined by those co-inventors indicated on invention
disclosure forms and/or individuals named in research grants obtained by Drs.
Bristow, Leinwand or Perryman) ("INVENTIONS"). ULEHI shall disclose to LICENSEE
in reasonable written detail any such Invention not later than fifteen (15) days
after ULEHI's Technology Transfer Office receives notification from the
inventor(s) that such Invention has been made, and LICENSEE shall have nine (9)
months following receipt of such Invention disclosure to exercise the option by
delivering to ULEHI written notice indicating that LICENSEE desires to exercise
the option. Upon such notice of exercise, LICENSEE shall (a) pay to ULEHI a
one-time technology access fee of [/\#/\], (b) reimburse previous and future
ULEHI expenses associated with related patent filings and prosecution, and (c)
issue a total of [/\#/\] (to be distributed to the inventor(s) of the
Invention), following which, all intellectual property related to such Invention
shall be deemed included in the Intellectual Property and Know-How, as
applicable, and subject to the terms and conditions of the License Agreement.

9. SECTION 13.7 shall be deleted in its entirety and replaced with the
following:

         13.7 In the event that this Agreement is terminated by ULEHI for any
reason, any sublicense granted by LICENSEE shall remain in full force and
effect, provided that the

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED

                                       3.
<PAGE>

sublicensee is in good standing and the sublicensee agrees to be bound to ULEHI
as licensor pursuant to the terms and conditions of such sublicense agreement.

10. APPENDIX A to the License Agreement shall be deleted in its entirety and
replaced with the revised version of Appendix A attached to this Third
Amendment.

11. Except as specifically amended by this Third Amendment, the terms and
conditions of the License Agreement shall remain in full force and effect. This
Third Amendment may be executed in two or more counterparts, each of which shall
be deemed an original, but all of which together shall constitute one and the
same instrument.

         IN WITNESS WHEREOF, the parties have duly executed this Third Amendment
as of the Third Amendment Date.

UNIVERSITY TECHNOLOGY                        MYOGEN, INC
CORPORATION

By: /s/ David L. Drake                       By: /s/ J. William Freytag
   -------------------------------------         -------------------------------
   David L. Drake, Executive Director            J. William Freytag, Ph.D.,
                                                 President

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED

                                       4.
<PAGE>

                                  APPENDIX A-1

<Table>
<Caption>
  ITEM       CASE NUMBER        INVENTORS                      TITLE                    U.S. APP. NO.    U.S. PATENT
  ----       -----------        ---------                      -----                    -------------    -----------
<S>          <C>            <C>                <C>                                      <C>              <C>
    1          IR 360       Raynolds/          Angiotensin-converting enzyme genetic                      5,800,990
                            Perryman           variant screens
    2           6077        Port/Bristow       Transgenic model and treatment for                         6,218,597
                                               heart disease
    3           7022        Leinwand/          Transgenic Model for Heart Failure                         6,353,151*
                            Vikstrom
    4           7076        Bristow/Port       Method for identifying adrenergic                          6,203,776*
                                               receptor antagonists having good
                                               tolerability
    5          [/\#/\]      [/\#/\]            [/\#/\]                                     [/\#/\]
    6           7080        Bristow            Method of treating heart failure                           5,998,458*
    7          [/\#/\]      [/\#/\]            [/\#/\]                                     [/\#/\]
    8          [/\#/\]      [/\#/\]            [/\#/\]                                     [/\#/\]
</Table>

* Including related foreign equivalents

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED

                                       1.

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00061-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00061-of-00352.parquet"}]]