Long-term treatment of pulmonary arterial HTN (PAH) in adult patients w/ WHO functional class II-III, including idiopathic & heritable PAH, PAH associated w/ connective tissue disorders, & PAH associated w/ corrected simple congenital heart disease, either as combination therapy in patients insufficiently controlled w/ endothelin receptor antagonist &/or phosphodiesterase type 5 inhibitor, or as monotherapy in patients who are not candidates for these therapies.