Epoprostenol for Injection in Pulmonary Arterial Hypertension - Extension of AC-066A401

Inclusion Criteria: 1. Signed informed consent prior to initiation of any study-mandated procedure 2. Patients who completed participation in study AC-066A401 3. Patients who have not obtained authorization for commercial ACT-385781 and Flolan at the time of ending participation in study AC-066A401 Exclusion Criteria: 1. Patients who prematurely discontinued study drug in study AC-066A401 2. Patients for whom continued treatment with either ACT-385781 and Flolan is no longer considered appropriate 3. Known hypersensitivity to the investigational drug or comparative drug or drugs of the same class, or any of their excipients 4. Any known factor or disease that might interfere with treatment compliance, study conduct or interpretation of the results such as drug or alcohol dependence or psychiatric disease 5. Known concomitant life-threatening disease with a life expectancy \< 12 months