Safety and Efficacy Study of Ambrisentan in Subjects With Pulmonary Hypertension

Summarized Inclusion Criteria:

1. 18 years of age or older

2. Current diagnosis of PH associated with an acceptable etiology as outlined in theprotocol, including: PH due to the following etiologies: 1) PAH including idiopathicand familial PAH and PAH associated with collagen vascular disease, congenitalsystemic-to-pulmonary shunts (including Eisenmenger's syndrome), humanimmunodeficiency virus (HIV) infection, drugs and toxins, thyroid disorders, glycogenstorage disease, Gaucher disease, hemoglobinopathies, and splenectomy (WHO Group 1);

2. PH associated with lung diseases and/or hypoxemia, including chronic obstructivepulmonary disease (COPD), interstitial lung disease (ILD), sleep-disordered breathing,and alveolar hypoventilation disorders (WHO Group 3); 3) PH due to proximal or distalchronic thromboembolic obstruction (WHO Group 4); and 4) PH due to sarcoidosis (WHOGroup 5).

3. Stable regimen (within four weeks) of chronic prostanoid, PDE-5 inhibitor, calciumchannel blocker, or 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductaseinhibitor therapy

4. Right heart catheterization completed prior to screening must meet pre-specifiedcriteria

5. Female participants of childbearing potential must have a negative serum pregnancytest and must agree to use a reliable double method of contraception until studycompletion and for at least four weeks following their final study visit.

6. Male participants must be informed of the potential risks of testicular tubularatrophy and infertility associated with taking ambrisentan and queried regarding hisunderstanding of the potential risks as described in the Informed Consent Form.

Summarized Exclusion Criteria:

1. Participation in a previous clinical study with ambrisentan

2. Bosentan or sitaxsentan use within four weeks prior to the screening visit

3. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) lab value that isgreater than 3 times the upper limit of normal at the screening visit

4. Pulmonary function tests not meeting the following pre-specified criteria: 1) meanpulmonary arterial pressure (PAP) >= 25 mm Hg; 2) PVR > 3 mm Hg/L/min; 3) pulmonarycapillary wedge pressure (PCWP) or left ventricle end diastolic pressure (LVEDP) < 15mm Hg; 4) total lung capacity (TLC) >= 70% of predicted normal for participantswithout ILD or >= 60% of predicted normal in participants with ILD; forced expiratoryvolume in 1 second (FEV1) >= 65% of predicted normal in participants without COPD or >= 50% of predicted normal in participants with COPD

5. Contraindication to treatment with endothelin receptor antagonist (ERA)

6. History of malignancies other than basal cell carcinoma of the skin or in situcarcinoma of the cervix within the past five years

7. Female participant who is pregnant or breastfeeding