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

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

Ambrisentan has demonstrated a statistically significantimprovement in 6MWD in prior clinical trials in patients withpulmonary arterial hypertension (PAH), including a Phase 2 trial andtwo Phase 3, placebo-controlled, multi-center trials. The results fromthese prior trials form the foundation of the ambrisentan New DrugApplication (NDA), which is expected to be submitted to the U.S. Foodand Drug Administration (FDA) in the fourth quarter of 2006. TheARIES-3 trial is evaluating ambrisentan in pulmonary hypertension, oneof several additional indications beyond PAH in which ambrisentan mayhave utility. Myogen does not anticipate including data from theARIES-3 trial in the original ambrisentan NDA submission.

"This study will evaluate the safety and efficacy of ambrisentanin both a broader pulmonary hypertension patient population and intraditional PAH patients," said Dr. Michael J. Gerber, Senior VicePresident, Clinical Development and Regulatory Affairs. "The efficacyand safety of ambrisentan observed in the traditional PAH population,and the need for effective therapy in pulmonary hypertensionassociated with other causes, merits evaluation of ambrisentan inthese 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 chronicthromboembolic disease or sickle cell disease; PH associated withchronic obstructive pulmonary disease (COPD); PAH associated withcongenital heart defects; and PAH associated with HIV infection. Thetrial will also enroll patients with PAH receiving prostacyclin orsildenafil therapy at baseline, and patients who previouslydiscontinued either bosentan, sitaxsentan, or both, due to liverfunction test abnormalities.

About Pulmonary Hypertension (PH)

Pulmonary hypertension is a highly debilitating diseasecharacterized by severe constriction of the blood vessels in the lungsleading to very high pulmonary arterial pressures. These highpressures make it difficult for the heart to pump blood through thelungs to be oxygenated. Patients with PH suffer from extreme shortnessof breath as the heart struggles to pump against these high pressurescausing such patients to ultimately die of heart failure. PH iscategorized into five subgroups: PAH, PH with left-heart disease, PHassociated with lung diseases and/or hypoxemia, PH due to chronicthrombotic and/or embolic disease and miscellaneous forms of PH.

About Ambrisentan

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

Ambrisentan is a non-sulfonamide, propanoic acid-class, type-Aselective endothelin receptor antagonist. Endothelin is a smallpeptide hormone that plays a critical role in the control of bloodflow and cell growth. Elevated endothelin blood levels are associatedwith several cardiovascular disease conditions, including PAH, chronicrenal disease, coronary artery disease, hypertension and chronic heartfailure. Myogen believes that agents that block the detrimentaleffects of endothelin may provide significant benefits in thetreatment of these conditions.

About Myogen

Myogen has two product candidates in late-stage clinicaldevelopment: ambrisentan for the treatment of patients with pulmonaryarterial hypertension (PAH) and darusentan for the treatment ofpatients with resistant hypertension. Myogen and GlaxoSmithKline haveentered into a global PAH collaboration in which Myogen has marketingand distribution rights to GlaxoSmithKline's Flolan(R) (epoprostenolsodium) for Injection in the United States and GlaxoSmithKline haslicensed ambrisentan from Myogen for all territories outside of theUnited States, where Myogen retains exclusive rights. Myogen alsoconducts a target and drug discovery research program focused on thedevelopment of disease-modifying drugs for the treatment of chronicheart failure and related cardiovascular disorders. Please visitMyogen's website at www.myogen.com.

Safe Harbor Statement

This press release contains forward-looking statements thatinvolve significant risks and uncertainties, including statementsrelating to ambrisentan clinical data, the enrollment and completionof the Company's ARIES-3 clinical trials and expected timing ofsubmission of the ambrisentan NDA. Actual results could differmaterially from those projected and the Company cautions investors notto place undue reliance on the forward-looking statements contained inthis release.

Among other things, the projected enrollment of the Company'sclinical trials, including the ARIES-3 trial, and the timing of therelease of results of clinical trials may be affected by difficultiesor delays, including difficulties or delays in patient enrollment,patient treatment, data collection and data analysis. The results ofMyogen's prior clinical trials of its product candidates, includingambrisentan, do not necessarily predict the results of future clinicaltrials. Preliminary results may not be confirmed upon full analysis ofthe detailed results of a trial. There can be no assurance thatMyogen's product candidates, including ambrisentan, have better safetyprofiles than competing products, including a lower incidence of livertoxicity or liver toxicity that is not dose dependent. Among otherthings, Myogen's results may be affected by competition from otherpharmaceutical and biotechnology companies, Myogen's ability tosuccessfully develop and market its current products, difficulties ordelays in its clinical trials, regulatory developments involvingcurrent and future products and its effectiveness at managing itsfinancial resources. If the Company's product candidates, includingambrisentan and darusentan, do not meet the safety or efficacyendpoints in clinical evaluations, they will not receive regulatoryapproval and the Company will not be able to market them. Even ifMyogen's product candidates meet safety and efficacy endpoints,regulatory authorities may not approve them, or the Company may facepost-approval problems that require the withdrawal of its productsfrom the market. If the Company is unable to raise additional capitalwhen required or on acceptable terms, it may have to significantlydelay, scale back or discontinue one or more of its drug developmentor discovery research programs.

Additional risks and uncertainties relating to the company and itsbusiness can be found in the "Risk Factors" section of Myogen's Form10-K for the year ended December 31, 2005, and Myogen's periodicreports on Form 10-Q and Form 8-K. Myogen does not undertake anyobligation to update any forward-looking statements contained in theanticipated presentation as a result of new information, future eventsor otherwise. The company cautions investors not to place unduereliance on the forward-looking statements contained in this pressrelease or the presentation. No forward-looking statement can beguaranteed and actual events and results may differ materially fromthose projected.