Main Inclusion Criteria:

  1. Males and females aged 18-75 years, inclusive
  2. Diagnosis of WHO Group I PAH
  3. Be on stable PAH therapy
  4. Has PFTs within 6 Months prior to the start of Screening with no evidence of significant parenchymal lung disease. Parenchymal lung disease is defined as FVE1 ≤ 70% (predicted); FEV1/FVC≤ 70% (predicted); TLC < 70%

Main Exclusion Criteria:

  1. Newly diagnosed PAH with no disease-specific PAH therapy
  2. Male patients with a QTc > 450ms; Female patients with QTc > 470ms on screening ECG
  3. Use of chronic administration (defined as >30 days)of a prostacyclin or prostacyclin analogue within 3 months of Screening