Document:

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                                                                   EXHIBIT 10.37

                             [..**..] 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 THE LICENSE AGREEMENT (ENOXIMONE)
                                 BY AND BETWEEN
                          AVENTIS PHARMACEUTICALS INC.
                     (FORMERLY HOECHST MARION ROUSSEL, INC.)
                                       AND
                                  MYOGEN, INC.

         This Third Amendment to the License Agreement (Enoximone) by and
between Aventis Pharmaceuticals Inc. (formerly Hoechst Marion Roussel, Inc.
("HMR")) and Myogen, Inc. effective October 1, 1998 ("Third Amendment" and
"License Agreement" respectively) dated the 27th day of January 2005 and
effective the 1st day of January, 2005 (the "Effective Date of the Third
Amendment"), by and between Aventis Pharmaceuticals Inc., a Delaware corporation
with a principal office at 300 Somerset Corporate Blvd. Bridgewater, New Jersey
08807 ("Aventis"), and Myogen, Inc., a Delaware corporation with a principal
office at 7575 W. 103rd Avenue, suite 102, Westminster, CO 80021-5426 ("Myogen")
(each individually a "Party" or collectively "Parties").

                                   BACKGROUND

         HMR and Myogen entered into the License Agreement effective October 1,
1998 under which Myogen obtained an exclusive worldwide license under the HMR
Patents, HMR Know-how and Joint Patents to develop and commercialize Enoximone.
HMR also transferred to Myogen, on or about the Transfer Date, any and all of
HMR's rights under the existing HMR Trademarks in several countries around the
world, including the United Kingdom and the Benelux countries.

         Effective November 23, 1999, the Parties entered into the First
Amendment to the License Agreement (the "First Amendment") under which Myogen
granted to HMR the right to co-market the Product containing the oral form of
Enoximone ("Oral Enoximone") in Europe. This grant was terminated under the
Second Amendment to the License Agreement (the "Second Amendment"), which was
effective June 2, 2003. The Second Amendment also provided for a certain royalty
to be paid by Myogen to Aventis in the event the Net Sales of Oral Enoximone in
Europe reached or exceeded the threshold set forth in the amendment.

         Myogen is currently commercializing Perfan(R) i.v. (enoximone) ("Perfan
i.v.") in various countries around the world, including the United Kingdom,
Belgium and other countries in Europe. Myogen is also undertaking two pivotal
Phase III clinical trials for Oral Enoximone and, depending upon the outcome of
these studies, anticipates seeking marketing authorization approval in Europe.

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         Aventis and its Affiliates were acquired by Sanofi-Synthelabo, a
pharmaceutical company organized under the laws of France, in or about August
2004, and, shortly thereafter, Sanofi-Synthelabo changed its name to
sanofi-aventis. In approving the acquisition, the Commission des Communautes
Europeennes (the "EU Commission") requested that Aventis divest certain rights
related to Enoximone specifically in the United Kingdom and Belgium. The Parties
desire to modify the terms of the License Agreement, the First Amendment and the
Second Amendment (hereinafter collectively referred to as the "License
Agreement") in order to effectuate this request.

         NOW, THEREFORE, in consideration of the mutual promises, covenants and
agreements hereinafter set forth, the sufficiency of which is hereby
acknowledged, and intending to be legally bound, the Parties to this Third
Amendment mutually agree as follows:

1.       INTERPRETATION. Unless the context of this Third Amendment otherwise
requires, (i) words of any gender include each other gender; (ii) words using
the singular or plural number also include the plural or singular number,
respectively; (iii) the terms "hereof," "herein," "whereby" and derivative or
similar words refer to this Third Amendment; and (iv) the term "Article" refers
to the specified Article of this Third Amendment. Whenever this Third Amendment
refers to a number of days, such number shall refer to calendar days unless
otherwise specified. Capitalized terms not otherwise defined in this Third
Amendment shall have the meaning set forth in the License Agreement. To the
extent there are any conflicts or inconsistencies between this Third Amendment
and the License Agreement, this Third Amendment shall control. Except as
expressly modified by this Third Amendment, the terms and conditions of the
License Agreement shall remain unchanged and in full force and effect.

2.       LIMITED EUROPEAN COUNTRIES; TERMINATED COUNTRIES.

         (a) The term "Limited European Countries" means Austria, Denmark,
Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands,
Portugal, Spain, and Sweden. The term "Limited European Country" means a country
within the Limited European Countries.

         (b) The term "Terminated Countries" as defined under Sections 1.36,
9.3.1 and 9.3.2 shall not include the United Kingdom and Belgium.

3.       NO ROYALTIES IN U.K. AND BELGIUM. Notwithstanding anything in the
License Agreement or this Third Amendment to the contrary, as of the Effective
Date of the Third Amendment, Myogen shall have no obligation to pay earned
royalties on any Product, whether on Net Sales or otherwise, in the United
Kingdom and Belgium. For purposes of clarity, as of the Effective Date of the
Third Amendment, Myogen has no further obligation to pay royalties to Aventis
for sales of Perfan i.v. or Oral Enoximone within the United Kingdom and
Belgium. Myogen also has no obligation, as of the Effective Date of the Third
Amendment, to report Net Sales of any Product to Aventis in the United Kingdom
and Belgium. In addition, Myogen has no obligation under Section 3.8.2 of the
License Agreement to deliver to Aventis a report containing information with
respect to Regulatory Filings in the United Kingdom and Belgium or to maintain
records under Section 3.8.3 with respect to Development activities in the United
Kingdom and Belgium.

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4.       SECTION 4.1 AND SECTION 2.3.2.

         (a) The Parties acknowledge and agree that Myogen has, prior to the
Effective Date of the Third Amendment, made all payments and taken all other
actions required by Sections 4.1(a) through 4.1(e) of the License Agreement.

         (b) The Parties acknowledge and agree that Section 4.1(f) of the
License Agreement only obligates Myogen to pay Aventis royalties on Net Sales of
Perfan i.v. in the Limited European Countries. Section 4.1(f) does not obligate
Myogen to pay royalties on the Net Sales of Oral Enoximone in the Limited
European Countries. The Parties further acknowledge and agree that (i) Section
4.2 of the License Agreement (as amended and restated below) only concerns and
relates to the sale of any Product, including Perfan i.v. and Oral Enoximone, in
any Territory other than Europe, and (ii) Section 4.3 of the License Agreement
(as amended and restated below) only concerns and relates to the sale of any
Additional Product (as defined below) in the Limited European Countries.

         (c) Section 4.1(f) of the License Agreement is amended and restated to
read as follows:

                  "(f) Beginning on the Effective Date and ending October 1,
         2011, Myogen will pay to Aventis, on a quarterly basis within 60 days
         after the end of each calendar quarter, periodic payments equal to
         [..**..] of Net Sales of Perfan i.v. in the Limited European Countries
         that occurred in the immediately preceding calendar quarter."

         (d) Section 2.3.2 of the License Agreement is amended and restated to
read as follows:

         "2.3.2   SUBLICENSE FEES AND PAYMENTS.

                  (a) At such time that Sublicense Fees and Payments (as defined
         below) exceed [..**..], Myogen shall pay to Aventis [..**..] of the
         Sublicense Fees and Payments in excess of the initial [..**..]. Myogen
         shall pay Sublicense Fees and Payments to Aventis within ten (10) days
         of Myogen's receipt of the corresponding payment from the applicable
         Sublicensee (as defined below).

                  (b) Myogen shall make certain that any sublicense agreement,
         under which a Sublicensee receives (x) a sublicense under Myogen's
         license under this Agreement in the United Kingdom and/or Belgium and
         (y) one or more other country in the Territory, clearly and equitably
         aggregates Sublicense Fees, Signing Fees, Milestone Payments and Equity
         Payments (as those terms are defined below) between the United Kingdom
         and/or Belgium (as the case may be) and such other country or countries
         in the Territory.

                  (c) Definitions.

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                           (i) "Sublicense Fees and Payments" mean the aggregate
                  of Sublicense Fees, Signing Payments, Milestone Payments and
                  Equity Payments to Myogen from Sublicensees. Sublicense Fees
                  and Payments shall not include any Sublicense Fees, Signing
                  Fees, Milestone Payments and Equity Payments that Myogen
                  receives from Sublicensees specifically related to the United
                  Kingdom and Belgium.

                           (ii) "Sublicense Fees" mean any lump sum fees paid by
                  a Sublicensee to Myogen.

                           (iii) "Signing Fees" means fees received by Myogen
                  from a Sublicensee upon signing of the sublicense agreement.

                           (iv) "Milestone Payments" means payments received by
                  Myogen from a Sublicensee that are payable upon achievement of
                  a particular milestone or goal.

                           (v) "Equity Payments" means amounts received by
                  Myogen for investments by the Sublicensee in Myogen to obtain
                  an equity position in Myogen in connection with Myogen
                  sublicensing activity.

                           (vi) "Sublicensee" means a Third Party that enters
                  into a sublicense agreement with Myogen providing a sublicense
                  to such Third Party under Myogen's license provided by this
                  Agreement.

                  (d) Notwithstanding any other provision contained in this
         Agreement, Sublicense Fees and Payments, Sublicense Fees, Signing Fees
         and Milestone Payments shall not include (i) any royalties on sales of
         Product received by Myogen from the Sublicensee, (ii) any payments to
         Myogen by the Sublicensee for research, development, clinical,
         manufacturing and regulatory work performed by Myogen during the term
         of the sublicense agreement (the "Myogen Sublicensee Services"),
         provided any such payments to Myogen by the Sublicensee for the Myogen
         Sublicensee Services are under the sublicense agreement and made at
         fair market value, and (iii) any loans provided by the Sublicensee to
         Myogen, provided Myogen is contractually obligated to fully repay such
         loans with interest at fair market rates."

5.       ROYALTIES IN TERRITORIES OTHER THAN EUROPE.  Section 4.2 of the License
Agreement is amended and restated to read as follows:

         "4.2     TERRITORY OTHER THAN EUROPE.

                  (a) Except as otherwise set forth in Sections 4.2(b) through
         (f) below, with respect to markets in the Territory other than the
         Limited European Countries and in consideration of the rights granted
         by Aventis under this Agreement, and provided that an HMR Patent is
         issued in one or more such markets containing a claim which would, but
         for a license granted in the Agreement, be infringed by Myogen's
         activities relating to such Product, Myogen will pay to Aventis, on a
         quarterly basis within sixty (60) days

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         after the end of each calendar quarter, periodic payments equal to
         [..**..] of Net Sales in such markets that occurred in the immediately
         preceding calendar quarter.

                  (b) Except as otherwise provided in Sections 4.2(c) or (d)
         below, in the event that in any country other than a Limited European
         Country there is no claim of an issued and unexpired HMR Patent which
         would, but for a license granted in the Agreement, be infringed by
         Myogen's activities relating to a Product or such HMR Patent expires in
         such country, the Net Sales royalty percentage set forth in Section
         4.2(a) above relating to such Product shall be reduced in such country
         to [..**..] of the Net Sales royalty percentage set forth in Section
         4.2(a) but shall in no event be less than [..**..] until the tenth
         (10th) anniversary of the first commercial sale of the relevant Product
         in that country, after which time all royalty obligations in that
         country relating to such Product shall cease (subject to Sections
         4.2(c) and (d) below).

                  (c) Subject to Sections 4.2(d) and (e) below, in the event
         that prior to the tenth (10th) anniversary of the first commercial sale
         of a relevant Product in any country other than a Limited European
         Country, an HMR Patent is issued in such country containing a claim
         which would, but for a license granted in the Agreement, be infringed
         by Myogen's activities relating to such Product, then, from that date
         forward, the royalty percentage relating to such Product in such
         country shall increase to the Net Sales royalty percentage as set forth
         under Section 4.2(a) above (that is, to [..**..] of Net Sales) and
         Myogen shall pay this increased royalty to Aventis in such country as
         set forth in Section 4.2(a) until such time as (i) there is no claim of
         an issued and unexpired HMR Patent in such country which would, but for
         a license granted in the Agreement, be infringed by Myogen's activities
         relating to such Product, or (ii) such HMR Patent expires, after which
         time all royalty obligations in that country relating to such Product
         shall cease. In the event that either of the contingencies set forth in
         (i) or (ii) in the preceding sentence occur prior to the tenth (10th)
         anniversary of the first commercial sale of a relevant Product in such
         country, then the Net Sales royalty percentage, from such contingency
         date, shall be at the rate set forth in Section 4.2(b) above until such
         tenth (10th) anniversary.

                  (d) Notwithstanding the foregoing and the existence of any HMR
         Patent issued in a country that is not a Limited European Country
         containing a claim which would, but for a license granted in the
         Agreement, be infringed by Myogen's activities relating to such Product
         in such country, in the event that the marketing of a generic version
         of such Product in such country is otherwise prohibited by applicable
         law, rule or regulation (as determined in good faith by the Parties),
         then until the earlier of (i) the date on which the marketing of a
         generic version of the Product in such country is no longer prohibited
         by applicable law, rule or regulation, or (ii) one (1) year from the
         date on which the relevant HMR Patent was issued in such country, the
         Net Sales royalty percentage in such country set forth in Section
         4.2(a) above relating to such Product shall be reduced by [..**..] but
         shall in no event be less than [..**..], after which time all royalty
         obligations relating to such Product in such country, if any, shall be
         governed by Sections 4.2(a), (b) and (c) above and Sections 4.2(e) and
         (f) below, as applicable.

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                  (e) Notwithstanding any other provision contained in this
         Section 4.2, in the event there is a claim of an issued and unexpired
         HMR Patent in any country other than a Limited European Country which
         would, but for a license granted in the Agreement, be infringed by
         Myogen's activities, but, notwithstanding, a generic version of a
         Product is marketed in such country, the royalty percentage under
         Section 4.2(a) for that Product will be reduced, in that country, to
         [..**..] of the Net Sales royalty percentage set forth in Section
         4.2(a) but shall in no event be less than [..**..].

                  (f) The Parties acknowledge that the reductions in royalty
         rates in Sections 4.2(b), (c), (d) and (e) above are not cumulative so
         that there shall not be more than one reduction in royalty rates at any
         one time in any country based upon any of the occurrences in Sections
         4.2(b), (c), (d) and (e). By way of example, in the event that there is
         no relevant HMR Patent in a country other than a Limited European
         Country and the royalty rate is [..**..] the rate set forth in Section
         4.2(a) above, and, some time thereafter, a law comes into effect in
         such country prohibiting the marketing of a generic version of such
         Product, the royalty rate shall not otherwise be further reduced."

6.       ROYALTIES IN LIMITED EUROPEAN COUNTRIES. Section 4.3 of the License
Agreement is amended and restated to read as follows:

         "4.3     ROYALTIES IN LIMITED EUROPEAN COUNTRIES.

                  (a) Except as otherwise set forth in Sections 4.3(b) through
         (f) below, beginning two (2) years after the date on which a Product
         that has not been approved in any country in Europe as of the Effective
         Date of the Third Amendment (an "Additional Product"), including but
         not limited to Oral Enoximone but excluding Perfan i.v., is approved in
         a Limited European Country (such two (2) year anniversary, the "Limited
         European Payment Initiation Date"), and provided that an HMR Patent is
         issued in one or more Limited European Countries containing a claim
         which would, but for a license granted in the Agreement, be infringed
         by Myogen's activities relating to such Additional Product, Myogen will
         pay to Aventis on a quarterly basis within sixty (60) days after the
         end of each calendar quarter, periodic payments equal to (i) [..**..]
         of Net Sales (the "Net Sales Royalty Percentage") of the Additional
         Products less than [..**..] during the calendar year in such Limited
         European Countries, and (ii) [..**..] on incremental Net Sales of the
         Additional Products that equal or exceed [..**..] in a calendar year in
         such Limited European Countries.

                  (b) Except as otherwise provided in Sections 4.3(c) or (d)
         below, in the event that in a Limited European Country there is no
         claim of an issued and unexpired HMR Patent which would, but for a
         license granted in the Agreement, be infringed by Myogen's activities
         relating to such Additional Product or such HMR Patent expires in a
         Limited European Country, the Net Sales Royalty Percentages set forth
         in Section 4.3(a) above relating to such Additional Product shall be
         reduced in such Limited European Country to [..**..] of the Net Sales
         Royalty Percentages set forth in Section 4.3(a) until the tenth (10th)
         anniversary of the Limited European Payment Initiation Date, after
         which

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         time all royalty obligations in that Limited European Country relating
         to such Additional Product shall cease (subject to Sections 4.3(c) and
         (d) below).

                  (c) Subject to Sections 4.3(d) and (e) below, in the event
         that prior to the tenth (10th) anniversary of the Limited European
         Payment Initiation Date, an HMR Patent is issued in a Limited European
         Country containing a claim which would, but for a license granted in
         the License Agreement, be infringed by Myogen's activities relating to
         such Additional Product, then, from that date forward, the royalty
         percentage relating to such Additional Product in such country shall
         increase to the Net Sales Royalty Percentages as set forth under
         Section 4.3(a) above and Myogen shall pay this increased royalty to
         Aventis in such Limited European Country as set forth in Section 4.3(a)
         until such time as (i) there is no claim of an issued and unexpired HMR
         Patent in such Limited European Country which would, but for a license
         granted in the Agreement, be infringed by Myogen's activities relating
         to such Additional Product, or (ii) such HMR Patent expires, after
         which time all royalty obligations in that Limited European Country
         relating to such Additional Product shall cease. In the event that
         either of the contingencies set forth in (i) or (ii) in the preceding
         sentence occur prior to the tenth (10th) anniversary of the Limited
         European Payment Initiation Date, then the Net Sales Royalty
         Percentages, from such contingency date, shall be at the rate set forth
         in Section 4.3(b) above until such tenth (10th) anniversary.

                  (d) Notwithstanding the foregoing and the existence of any HMR
         Patent issued in a Limited European Country containing a claim which
         would, but for a license granted in the Agreement, be infringed by
         Myogen's activities relating to such Additional Product in such
         country, in the event that the marketing of a generic version of such
         Additional Product in such Limited European Country is otherwise
         prohibited by applicable law, rule or regulation (as determined in good
         faith by the Parties), then until the earlier of (i) the date on which
         the marketing of a generic version of the Additional Product in such
         Limited European Country is no longer prohibited by applicable law,
         rule or regulation, or (ii) three (3) years from the Limited European
         Payment Initiation Date, the Net Sales Royalty Percentages relating to
         such Additional Product in such country set forth in Section 4.3(a)
         above shall be reduced to [..**..] of the Net Sales Royalty Percentages
         set forth in Section 4.3(a) (that is, to [..**..] under Subsection
         4.3(a)(i) and to [..**..] under Subsection 4.3(a)(ii)), after which
         time all royalty obligations in such Limited European Country, if any,
         shall be governed by Sections 4.3(a), (b) and (c) above and Sections
         4.3(e) and (f) below, as applicable.

                  (e) Notwithstanding any other provision contained in this
         Section 4.3, in the event there is a claim of an issued and unexpired
         HMR Patent in a Limited European Country which would, but for a license
         granted in the Agreement, be infringed by Myogen's activities related
         to an Additional Product, but, notwithstanding, a generic version of
         such Additional Product is marketed in such country, the royalty
         percentage under Section 4.3 (a) for that Additional Product will be
         reduced, in that Limited European Country, to [..**..] of the Net Sales
         Royalty Percentages set forth in Section 4.3(a) (that is, to [..**..]
         under Subsection 4.3(a)(i) and to [..**..] under Subsection
         4.3(a)(ii)).

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                  (f) The Parties acknowledge that the Net Sales Royalty
         Percentages reductions in Sections 4.3(b), (c), (d) and (e) above are
         not cumulative so that there shall not be more than one reduction in
         royalty rates at any one time in any Limited European Country based
         upon any of the occurrences. By way of example, in the event that there
         is no relevant HMR Patent in a Limited European Country and the Net
         Sales Royalty Percentages are [..**..] the rates set forth in Section
         4.3(a) above, and, some time thereafter, a law comes into effect in
         such country prohibiting the marketing of a generic version of such
         Additional Product, the Net Sales Royalty Percentages shall not be
         otherwise further reduced."

7.       SECTION 4.4.  Section 4.4 of the License Agreement is amended and
restated as follows:

         "4.4     INTENTIONALLY OMITTED."

8.       MYOGEN COOPERATION DUE TO TERMINATION FOR MATERIAL BREACH. Section
9.4(b)(iv) of the License Agreement is amended and restated as follows:

                  "(iv) Myogen shall cooperate in the transfer to Aventis of all
     NDAs, Drug Approval Applications and Regulatory Approvals related to
     Enoximone, and shall take such other actions and execute such other
     instruments, assignments and documents as may be necessary to effect the
     transfer of rights hereunder to Aventis. Notwithstanding the preceding,
     Myogen shall have no obligation to transfer to Aventis any NDAs, Drug
     Approval Applications and Regulatory Approvals related to Enoximone in the
     United Kingdom and Belgium."

9.       HMR TRADEMARKS IN THE UNITED KINGDOM AND BELGIUM. Article IX of the
License Agreement is amended to add the following Section 9.8:

                  "9.8 HMR TRADEMARKS IN THE UNITED KINGDOM AND BELGIUM.
     Notwithstanding anything to the contrary in the Agreement, Aventis'
     transfer under Section 4.1(c) of the Agreement of the HMR Trademarks in the
     United Kingdom and the Benelux countries (Belgium, the Netherlands and
     Luxembourg) is, as of the Effective Date of the Third Amendment, perpetual
     and irrevocable. Under no circumstance, including termination of the
     Agreement, whether due to Material Breach of the agreement by Myogen or
     otherwise, shall Myogen be obligated to transfer to Aventis its rights
     under the HMR Trademarks in the United Kingdom and the Benelux countries.
     It is understood between the Parties that the rights granted hereunder are
     limited to the United Kingdom and the Benelux countries and consequently,
     unless otherwise specifically permitted under the Agreement, Myogen shall,
     except as otherwise permitted by the Agreement, refrain from (i) using the
     HMR Trademarks or any other similar trademarks outside of the United
     Kingdom and the Benelux countries, (ii) making applications to register
     these trademarks or any other similar trademarks outside the United Kingdom
     and the Benelux countries, or (iii) challenge the rights Aventis or any of
     its Affiliates may have to these trademarks outside the United Kingdom and
     the Benelux countries."

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10.      HMR PATENTS, JOINT PATENTS AND HMR KNOW-HOW IN THE UNITED KINGDOM AND
BELGIUM.  Article IX of the License Agreement is amended to add the following
Section 9.9:

                  "9.9 HMR PATENTS, JOINT PATENTS AND HMR KNOW-HOW IN THE UNITED
     KINGDOM AND BELGIUM. Notwithstanding anything to the contrary in the
     Agreement, the license grants set forth in Sections 2.1 and 2.2 of the
     Agreement under the HMR Patents, Joint Patents and the HMR Know-how in the
     United Kingdom and Belgium are perpetual and irrevocable and shall survive
     termination of the Agreement. Section 2.3.1 shall not restrict Myogen from
     freely sublicensing the HMR Patents, Joint Patents and the HMR Know-how in
     the United Kingdom and Belgium. Nothing in the Agreement (including nothing
     in Section 6.6) shall restrict Myogen from freely assigning its rights
     under the HMR Patents, Joint Patents and the HMR Know-how to the extent,
     but only to the extent, the HMR Patents, Joint Patents and the HMR Know-how
     relate to the United Kingdom and Belgium."

11.      TERMINATION WITHOUT CAUSE (INCLUDING DENIAL OF PHASE III TRIALS). The
Parties acknowledge and agree that Myogen received consent from the FDA as
referenced in Section 9.5.1(b) of the License Agreement and that, therefore,
Myogen may not terminate the License Agreement pursuant to Section 9.5.1(b).
Except as expressly modified by this Third Amendment, the terms and conditions
of Section 9.5 of the License Agreement, including, without limitation, Myogen's
right to terminate the License Agreement without cause pursuant to Section
9.5.1(a), shall remain unchanged and in full force and effect.

12.      EU COMMISSION APPROVAL; CONDITION PRECEDENT. This Third Amendment and
its terms and conditions, including the license grant and corresponding transfer
of rights and assets hereunder, are subject to approval by the EU Commission.
Myogen agrees to use reasonable commercial efforts to cooperate with the EU
Commission and with Aventis in order to effectuate such approval and clearance
of the transaction contemplated under this Third Amendment in accordance with
the terms of this Third Amendment. The Parties shall diligently take all further
action reasonably necessary or useful and shall cooperate with each other in
order to carry out the purpose of this Third Amendment, including, but not
limited to, diligently undertaking any action reasonably necessary to satisfy as
quickly as possible the condition precedent referred to in this Section 12. To
the extent separate or particular documents or instruments are mutually agreed
by the Parties to be required or any other steps are reasonably necessary or
beneficial in connection therewith, the Parties agree to use reasonable
commercial efforts to execute such documents or instruments and to consummate
such steps promptly. In the event that the EU Commission informs sanofi-aventis
that it will not approve this Third Amendment, then the Parties, in good faith,
will use reasonable commercial efforts to promptly modify this Third Amendment
and to undertake any other steps so as to expeditiously obtain the approval of
the EU Commission. Notwithstanding any other provision contained in this Third
Amendment (including, without limitation, this Section 12), Myogen shall not be
required to take any action or agree to any material modification or material
amendment to the License Agreement or this Third Amendment or take any action
which requires Myogen to incur any material expense or make any material payment
not expressly contemplated by this Third Amendment or the License Agreement. In
the event that the Parties have timely and in good faith undertaken such actions
and the EU Commission continues to refuse to approve this Third Amendment, then
either Party may terminate this Third Amendment upon five (5) days prior written
notice and this Third

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Amendment shall be null and void. This Third Amendment, the transaction
contemplated herein and the transfer of ownership to the corresponding rights
and assets to Myogen shall have been approved by the European Commission, in
accordance with Articles 16 and 17 of the commitments signed by
Sanofi-Synthelabo on April 23, 2004 (Case M. 3354), as properly evidenced by
Aventis.

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         IN WITNESS WHEREOF, the Parties have caused this Third Amendment to be
executed by their duly authorized representatives as of the date first set forth
above.

MYOGEN , INC.

By: /s/ J. William Freytag
    ---------------------------

Name: J. William Freytag, Ph.D.

Title: CEO & President

AVENTIS PHARMACEUTICALS INC.

By: /s/ Juergen Lasowski
    ---------------------------

Name: Juergen Lasowski

Title: VP Business Dev. & Strategy

By: /s/ Gregory Irace
    ---------------------------

Name: Gregory Irace

Title: Senior Vice President, Finance

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                                       [..**..] CONFIDENTIAL TREATMENT REQUESTED<PAGE>
                                                                   EXHIBIT 10.38

                                  MYOGEN, INC.

                        2003 EMPLOYEE STOCK PURCHASE PLAN
                                    OFFERING

            ADOPTED BY THE BOARD OF DIRECTORS AS OF FEBRUARY 1, 2005

         In this document, capitalized terms not otherwise defined shall have
the same definitions of such terms as in the Myogen, Inc. 2003 Employee Stock
Purchase Plan.

1.       GRANT; OFFERING DATE.

         (A) The Board hereby authorizes a series of Offerings pursuant to the
terms of this Offering document.

         (B) The Offering shall begin on February 1, 2005 and shall end on
January 31, 2007, unless terminated earlier as provided below. Thereafter, an
Offering shall begin on the day after the last Purchase Date of the immediately
preceding Offering. The first day of an Offering is that Offering's "OFFERING
DATE." Each Offering shall be twenty-four (24) months in duration, with four (4)
Purchase Periods each of which shall be approximately six (6) months in length.
Except as provided below, a "PURCHASE DATE" is the last day of a Purchase Period
or of an Offering, as the case may be. The Offering shall consist of four (4)
Purchase Periods, with the first Purchase Period ending on July 31, 2005, the
second Purchase Period ending on January 31, 2006, the third Purchase Period
ending on July 31, 2006, and the fourth Purchase Period ending on January 31,
2007.

         (C) Notwithstanding the foregoing: (i) if any Offering Date falls on a
day that is not a Trading Day, then such Offering Date shall instead fall on the
next subsequent Trading Day, and (ii) if any Purchase Date falls on a day that
is not a Trading Day, then such Purchase Date shall instead fall on the
immediately preceding Trading Day.

         (D) Prior to the commencement of any Offering, the Board may change any
or all terms of such Offering and any subsequent Offerings. The granting of
Purchase Rights pursuant to each Offering hereunder shall occur on each
respective Offering Date unless prior to such date (i) the Board determines that
such Offering shall not occur, or (ii) no shares of Common Stock remain
available for issuance under the Plan in connection with the Offering.

         (E) If the Company's accountants advise the Company that the accounting
treatment of purchases under the Plan has changed in a manner that the Company
determines is detrimental to its best interests, then each Offering hereunder
that is then ongoing shall terminate as of the next Purchase Date (after the
purchase of stock on such Purchase Date) under such Offering.

         (F) Notwithstanding anything in this Section 1 to the contrary, if on
the first day of a new Purchase Period during the Offering the Fair Market Value
of a share of Common Stock is less than it was on the Offering Date for that
Offering, then that Offering shall immediately terminate and that day shall
become the Offering Date of a new Offering. Eligible Employees

<PAGE>

in the terminated Offering shall automatically be enrolled in the new Offering
that starts on such day.

2.       ELIGIBLE EMPLOYEES.

         (A) Each Employee of the Company or of a Subsidiary on the Offering
Date of an Offering hereunder (an "ELIGIBLE EMPLOYEE"), shall be granted a
Purchase Right on the Offering Date of such Offering.

         (B) Notwithstanding the foregoing, the following Employees shall not be
Eligible Employees or be granted Purchase Rights under an Offering:

             (I) part-time or seasonal Employees whose customary employment is
less than twenty (20) hours per week or less than five (5) months per calendar
year;

             (II) five percent (5%) stockholders (including ownership through
unexercised and/or unvested stock options) as described in Section 6(c) of the
Plan; or

             (III) Employees in jurisdictions outside of the United States if,
as of the Offering Date of the Offering, the grant of such Purchase Rights would
not be in compliance with the applicable laws of any jurisdiction in which the
Employee resides or is employed.

         (C) Notwithstanding the foregoing, each person who first becomes an
Eligible Employee during an Offering shall receive, on the day after the first
Purchase Date during that Offering, which occurs after the date such person
becomes an eligible employee, a Purchase Right under such Offering, which
Purchase Right shall thereafter be deemed to be a part of the Offering. Such
Purchase Right shall have the same characteristics as any Purchase Rights
originally granted under the Offering except that:

             (I) the date on which such Purchase Right is granted shall be the
"Offering Date" of such Purchase Right for all purposes except for the
application of the provision of Section 1(f) above (the application of which
shall be determined only by using the Offering Date of the ongoing Offering),
including determination of the exercise price of such Purchase Right; and

            (II) the Offering for such Purchase Right shall begin on its
Offering Date and end coincident with the end of the ongoing Offering.

3.       PURCHASE RIGHTS.

         (A) Subject to the limitations herein and the Plan, unless a lower
percentage has been set by the Board or a committee thereof prior to the
commencement of the Offering, a Participant's Purchase Right shall permit the
purchase of the number of shares of Common Stock purchasable with up to twenty
percent (20%) of such Participant's Earnings paid during the period of such
Offering beginning immediately after such Participant first commences
participation; provided, however, that no Participant may have more than twenty
percent (20%) of such Participant's Earnings applied to purchase shares of
Common Stock under all ongoing

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<PAGE>

Offerings under the Plan and all other plans of the Company and Related
Corporations that are intended to qualify as Employee Stock Purchase Plans.

         (B) For Offerings hereunder, "EARNINGS" means the base compensation
paid to an Eligible Employee, including all salary, wages and overtime pay
(including amounts elected to be deferred by such Eligible Employee, that would
otherwise have been paid, under any cash or deferred arrangement or other
deferred compensation program established by the Company or a Related
Corporation), but excluding commissions, bonuses, and other remuneration paid
directly to such Eligible Employee, profit sharing, the cost of employee
benefits paid for by the Company or a Related Corporation, education or tuition
reimbursements, imputed income arising under any Company or Related Corporation
group insurance or benefit program, traveling expenses, business and moving
expense reimbursements, income received in connection with stock options,
contributions made by the Company or a Related Corporation under any employee
benefit plan, and similar items of compensation.

         (C) Notwithstanding the foregoing, the maximum number of shares of
Common Stock that a Participant may purchase on any Purchase Date in an Offering
shall be such number of shares as has a Fair Market Value (determined as of the
Offering Date for such Offering) equal to (x) $25,000 multiplied by the number
of calendar years in which the Purchase Right under such Offering has been
outstanding at any time, minus (y) the Fair Market Value of any other shares of
Common Stock (determined as of the relevant Offering Date with respect to such
shares) that, for purposes of the limitation of Section 423(b)(8) of the Code,
are attributed to any of such calendar years in which the Purchase Right is
outstanding. The amount in clause (y) of the previous sentence shall be
determined in accordance with regulations applicable under Section 423(b)(8) of
the Code based on (i) the number of shares previously purchased with respect to
such calendar years pursuant to such Offering or any other Offering under the
Plan, or pursuant to any other Company or Related Corporation plans intended to
qualify as Employee Stock Purchase Plans, and (ii) the number of shares subject
to other Purchase Rights outstanding on the Offering Date for such Offering
pursuant to the Plan or any other such Company or Related Corporation Employee
Stock Purchase Plan.

         (D) The maximum aggregate number of shares of Common Stock available to
be purchased by all Participants under an Offering shall be the number of shares
of Common Stock remaining available under the Plan on the Offering Date. If the
aggregate purchase of shares of Common Stock upon exercise of Purchase Rights
granted under the Offering would exceed the maximum aggregate number of shares
available, the Board shall make a pro rata allocation of the shares available in
a uniform and equitable manner.

         (E) Notwithstanding the foregoing, the maximum number of shares of
Common Stock that a Participant may purchase on any Purchase Date during any
Offering shall not exceed Ten Thousand (10,000) shares.

4.       PURCHASE PRICE.

         The purchase price of shares of Common Stock under an Offering shall be
the lesser of: (i) eighty-five percent (85%) of the Fair Market Value of such

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<PAGE>

shares of Common Stock on the applicable Offering Date, or (ii) eighty-five
percent (85%) of the Fair Market Value of such shares of Common Stock on the
applicable Purchase Date, in each case rounded up to the nearest whole cent per
share.

5.       PARTICIPATION.

         (A) If an Eligible Employee intends to participate in an Offering, such
Eligible Employee shall elect his or her payroll deduction percentage on such
enrollment form as the Company provides. The completed enrollment form must be
delivered to the Company prior to the Offering Date of the applicable Offering,
unless a later time for filing the enrollment form is set by the Company for all
Eligible Employees with respect to a given Offering. Payroll deduction
percentages must be expressed in whole percentages of Earnings, with a minimum
percentage of one percent (1%) and a maximum percentage of twenty percent (20%).
Contributions may be made only by way of payroll deductions.

         (B) A Participant may increase or decrease (including a decrease to
zero percent (0%) his or her participation level at the beginning of each
Purchase Period and once during a Purchase Period. Any such increase or decrease
in participation level shall be made by delivering a notice to the Company or a
designated Subsidiary in such form as the Company provides at the beginning of
the Purchase Period or, with respect to the one change permitted during a
Purchase Period, prior to the ten (10) day period (or such shorter period of
time as determined by the Company and communicated to Participants) immediately
preceding the next Purchase Date of the Purchase Period for which it is to be
effective.

         (C) A Participant may withdraw from an Offering and receive a refund of
his or her Contributions (reduced to the extent, if any, such Contributions have
been used to acquire shares of Common Stock for the Participant on any prior
Purchase Date) without interest, at any time prior to the end of the Offering,
excluding only each ten (10) day period immediately preceding a Purchase Date
(or such shorter period of time determined by the Company and communicated to
Participants), by delivering a withdrawal notice to the Company or a designated
Subsidiary in such form as the Company provides. A Participant who has withdrawn
from an Offering shall not again participate in such Offering, but may
participate in subsequent Offerings under the Plan in accordance with the terms
of the Plan and the terms of such subsequent Offerings.

         (D) Notwithstanding the foregoing or any other provision of this
Offering document or of the Plan to the contrary, neither the enrollment of any
Eligible Employee in the Plan nor any forms relating to participation in the
Plan shall be given effect until such time as a registration statement covering
the registration of the shares under the Plan that are subject to the Offering
has been filed by the Company and has become effective.

         (E) Notwithstanding the foregoing or any other provision of this
Offering document or of the Plan to the contrary, each Eligible Employee who is
employed on the Offering Date automatically shall be enrolled in the Offering,
with a Purchase Right to purchase up to the number of shares of Common Stock
that are purchasable with 20% of the Eligible Employee's Earnings, subject to
the limitations set forth in Section 3 above. Each Eligible Employee shall be
provided a certain period of time, as determined by the Company in its sole
discretion, within which to elect to authorize payroll deductions for the
purchase of shares during the Offering

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<PAGE>

(which may be for a percentage that is less than or equal to 20% of the Eligible
Employee's Earnings, including zero percent (0%)).

6.       PURCHASES.

         Subject to the limitations contained herein, on each Purchase Date,
each Participant's Contributions (without any increase for interest) shall be
applied to the purchase of whole shares, up to the maximum number of shares
permitted under the Plan and the Offering.

7.       NOTICES AND AGREEMENTS.

         Any notices or agreements provided for in an Offering or the Plan shall
be given in writing, in a form provided by the Company, and unless specifically
provided for in the Plan or this Offering, shall be deemed effectively given
upon receipt or, in the case of notices and agreements delivered by the Company,
five (5) days after deposit in the United States mail, postage prepaid.

8.       EXERCISE CONTINGENT ON STOCKHOLDER APPROVAL.

         The Purchase Rights granted under an Offering are subject to the
approval of the Plan by the stockholders of the Company as required for the Plan
to obtain treatment as an Employee Stock Purchase Plan.

9.       OFFERING SUBJECT TO PLAN.

         Each Offering is subject to all the provisions of the Plan, and the
provisions of the Plan are hereby made a part of the Offering. The Offering is
further subject to all interpretations, amendments, rules and regulations which
may from time to time be promulgated and adopted pursuant to the Plan. In the
event of any conflict between the provisions of an Offering and those of the
Plan (including interpretations, amendments, rules and regulations which may
from time to time be promulgated and adopted pursuant to the Plan), the
provisions of the Plan shall control.

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