A Study Evaluating the Long-Term Efficacy and Safety of Ralinepag in Subjects With PAH Via an Open-Label Extension

Inclusion Criteria: 1. Evidence of a personally signed and dated informed consent form indicating that the subject has been informed of all pertinent aspects of the study prior to initiation of any study-related procedures. 2. Subjects who are willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures. 3. Completed the protocol-defined Study Drug Termination Visit or End of Study Visit procedures in the preceding ralinepag study. 4. Both male and female subjects agree to use a medically acceptable method of contraception throughout the entire study period from informed consent through the 30 day Follow-up Visit, if the possibility of conception exists. Eligible male and female subjects must also agree not to participate in a conception process (i.e., actively attempt to become pregnant or to impregnate, sperm donation, in vitro fertilization) during the study and for 30 days after the last dose of ralinepag. Exclusion Criteria: 1. Subjects who prematurely discontinued investigational medicinal product (IMP) due to a drug-related AE/SAE or tolerability issue in the preceding ralinepag study in which they were enrolled, or subjects who did not complete all protocol defined study procedures at a Study Drug Termination Visit or End of Study Visit in the preceding ralinepag study. 2. Subjects who withdrew consent during participation in another ralinepag study. 3. Female subjects who wish to become pregnant or who have a positive pregnancy test on Day 1 (OLE Entry Visit), or are lactating or breastfeeding. 4. Subjects who have undergone lung or heart/lung transplant or the initiation of long-term parenteral or inhaled therapy with a prostacyclin during the time since participation in their original ralinepag study. 5. Subjects who had an emergency unblinding procedure in a prior Phase 2 or 3 study.