Safety and Efficacy Study of Ambrisentan in Subjects with Pulmonary Hypertension

This is a long-term, open-label study of a new experimental drug called ambrisentan. The purpose of this study is to evaluate the safety and efficacy of ambrisentan in a broad population of subjects with pulmonary arterial hypertension (PAH). Secondarily, this study will evaluate the effects of ambrisentan on other clinical measures of PAH, long-term treatment success, and survival. Subjects will receive 5 mg ambrisentan each day by mouth for the first 24 weeks. Then, subjects may receive 2.5, 5, or 10 mg each day by mouth, based on investigator discretion as clinically indicated. Each day of study participation subjects will receive ambrisentan until the study is ended or the subject discontinues study participation. Subjects may continue to receive ambrisentan until such time as the investigator or subject chooses to stop ambrisentan treatment, the cumulative adverse event profile does not warrant continuation of the study, ambrisentan becomes commercially available, or Gilead Sciences, Inc., stops the study.