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

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.