Four patients, two with idiopathic PAH, one with familial PAH, and one with sarcoid-related PAH, died at 12, 14, 14, and 18 months, respectively, from the time of bosentan therapy initiation. Two patients died 5 and 14 months after tapering off epoprostenol, while the other two were unable to transition. At baseline, all four patients were in WHO/NYHA functional class II and had diminished 6MWDs (419, 358, 363, and 232 m, respectively). From prior right heart catheterizations, the mean PA pressures were 39, 43, 53, and 48 mm Hg, respectively, the mean PVRs were 821, 467, 1,500, and 496 dyne · s · cm−5, respectively, and the mean cardiac indexes were 1.63, 3.67, 1.2, and 2.65 L/min/m2, respectively. No indexes were identified that predicted subsequent mortality.