Main Inclusion Criteria:
1. Patients with WHO Group 1 PAH.
2. Mean pulmonary arterial pressure >25mm Hg at rest or mPAP >30mm Hg with exercise, with a pulmonary wedge pressure ≤18mm Hg.
3. Pulmonary vascular resistance ≥240 dynes sec cm-5
Main Exclusion Criteria:
1. Patients with PAH in WHO Groups II, III, IV, or V.
2. Patients without documentation of hemodynamic criteria for PAH via RHC.
3. Patients that do not meet the hemodynamic criteria for entry.