Patients with IPAH, HPAH, PAH-CTD and PAH-HIV meeting all inclusion and no exclusion criteria will be enrolled. An open label phase 1a study (evaluating dosage and safety) will be conducted. This will followed by a randomized double blind placebo controlled Phase 1b study after Data Safety and Monitoring Board (DSMB) review of the one-month safety data for all the Phase 1a subjects. All patients must have documented PAH diagnosed within the last 5 years and all need to be on stable background PAH specific agents for at least 4 months.