Myogen Initiates Open-Label Phase 3 Clinical Trial of Ambrisentan in Patients with Pulmonary Hypertension.

DENVER -- Myogen, Inc. (Nasdaq: MYOG), a biopharmaceutical company focused on the discovery, development and commercialization of small molecule therapeutics for the treatment of cardiovascular disorders, today announced the initiation of ARIES-3 (AMB-323), a Phase 3 long-term, open-label safety and efficacy study of ambrisentan in a broad population of patients with pulmonary hypertension (PH).

The primary objective of this study is to evaluate the effect of ambrisentan on exercise capacity in a broad population of patients with PH. The primary endpoint of the trial is the change from baseline in six-minute walk distance (6MWD) at week 24. Secondary endpoints include: clinical worsening of pulmonary hypertension, change from baseline in World Health Organization (WHO) functional class, SF-36(R) health survey and the Borg dyspnea index.

Ambrisentan has demonstrated a statistically significant improvement in 6MWD in prior clinical trials in patients with pulmonary arterial hypertension (PAH), including a Phase 2 trial and two Phase 3, placebo-controlled, multi-center trials. The results from these prior trials form the foundation of the ambrisentan New Drug Application (NDA), which is expected to be submitted to the U.S. Food and Drug Administration (FDA) in the fourth quarter of 2006. The ARIES-3 trial is evaluating ambrisentan in pulmonary hypertension, one of several additional indications beyond PAH in which ambrisentan may have utility. Myogen does not anticipate including data from the ARIES-3 trial in the original ambrisentan NDA submission.

"This study will evaluate the safety and efficacy of ambrisentan in both a broader pulmonary hypertension patient population and in traditional PAH patients," said Dr. Michael J. Gerber, Senior Vice President, Clinical Development and Regulatory Affairs. "The efficacy and safety of ambrisentan observed in the traditional PAH population, and the need for effective therapy in pulmonary hypertension associated with other causes, merits evaluation of ambrisentan in these non-traditional groups."

ARIES-3 will enroll up to 200 patients in PH subgroups, including: PH associated with interstitial lung disease (ILD); PH due to chronic thromboembolic disease or sickle cell disease; PH associated with chronic obstructive pulmonary disease (COPD); PAH associated with congenital heart defects; and PAH associated with HIV infection. The trial will also enroll patients with PAH receiving prostacyclin or sildenafil therapy at baseline, and patients who previously discontinued either bosentan, sitaxsentan, or both, due to liver function test abnormalities.

About Pulmonary Hypertension (PH)

Pulmonary hypertension is a highly debilitating disease characterized by severe constriction of the blood vessels in the lungs leading to very high pulmonary arterial pressures. These high pressures make it difficult for the heart to pump blood through the lungs to be oxygenated. Patients with PH suffer from extreme shortness of breath as the heart struggles to pump against these high pressures causing such patients to ultimately die of heart failure. PH is categorized into five subgroups: PAH, PH with left-heart disease, PH associated with lung diseases and/or hypoxemia, PH due to chronic thrombotic and/or embolic disease and miscellaneous forms of PH.

About Ambrisentan

Ambrisentan is an investigational drug being developed as a once daily oral therapy for patients with PAH and has been granted orphan drug designation for the treatment of PAH in both the United States and European Union. GlaxoSmithKline licensed commercial rights for ambrisentan outside of the United States.

Ambrisentan is a non-sulfonamide, propanoic acid-class, type-A selective endothelin receptor antagonist. Endothelin is a small peptide hormone that plays a critical role in the control of blood flow and cell growth. Elevated endothelin blood levels are associated with several cardiovascular disease conditions, including PAH, chronic renal disease, coronary artery disease, hypertension and chronic heart failure. Myogen believes that agents that block the detrimental effects of endothelin may provide significant benefits in the treatment of these conditions.

About Myogen

Myogen has two product candidates in late-stage clinical development: ambrisentan for the treatment of patients with pulmonary arterial hypertension (PAH) and darusentan for the treatment of patients with resistant hypertension. Myogen and GlaxoSmithKline have entered into a global PAH collaboration in which Myogen has marketing and distribution rights to GlaxoSmithKline's Flolan(R) (epoprostenol sodium) for Injection in the United States and GlaxoSmithKline has licensed ambrisentan from Myogen for all territories outside of the United States, where Myogen retains exclusive rights. Myogen also conducts a target and drug discovery research program focused on the development of disease-modifying drugs for the treatment of chronic heart failure and related cardiovascular disorders. Please visit Myogen's website at www.myogen.com.

Safe Harbor Statement

This press release contains forward-looking statements that involve significant risks and uncertainties, including statements relating to ambrisentan clinical data, the enrollment and completion of the Company's ARIES-3 clinical trials and expected timing of submission of the ambrisentan NDA. Actual results could differ materially from those projected and the Company cautions investors not to place undue reliance on the forward-looking statements contained in this release.

Among other things, the projected enrollment of the Company's clinical trials, including the ARIES-3 trial, and the timing of the release of results of clinical trials may be affected by difficulties or delays, including difficulties or delays in patient enrollment, patient treatment, data collection and data analysis. The results of Myogen's prior clinical trials of its product candidates, including ambrisentan, do not necessarily predict the results of future clinical trials. Preliminary results may not be confirmed upon full analysis of the detailed results of a trial. There can be no assurance that Myogen's product candidates, including ambrisentan, have better safety profiles than competing products, including a lower incidence of liver toxicity or liver toxicity that is not dose dependent. Among other things, Myogen's results may be affected by competition from other pharmaceutical and biotechnology companies, Myogen's ability to successfully develop and market its current products, difficulties or delays in its clinical trials, regulatory developments involving current and future products and its effectiveness at managing its financial resources. If the Company's product candidates, including ambrisentan and darusentan, do not meet the safety or efficacy endpoints in clinical evaluations, they will not receive regulatory approval and the Company will not be able to market them. Even if Myogen's product candidates meet safety and efficacy endpoints, regulatory authorities may not approve them, or the Company may face post-approval problems that require the withdrawal of its products from the market. If the Company is unable to raise additional capital when required or on acceptable terms, it may have to significantly delay, scale back or discontinue one or more of its drug development or discovery research programs.

Additional risks and uncertainties relating to the company and its business can be found in the "Risk Factors" section of Myogen's Form 10-K for the year ended December 31, 2005, and Myogen's periodic reports on Form 10-Q and Form 8-K. Myogen does not undertake any obligation to update any forward-looking statements contained in the anticipated presentation as a result of new information, future events or otherwise. The company cautions investors not to place undue reliance on the forward-looking statements contained in this press release or the presentation. No forward-looking statement can be guaranteed and actual events and results may differ materially from those projected.