A nonpeptide ET-A receptor antagonist (IC50s = 0.251, 0.316, 0.398, 251, and 630 nM for rat preparations of heart, bladder, kidney, lung, and cerebral cortex, respectively); inhibits ET-1-induced contraction of human pulmonary and radial arteries in vitro (Kd = 0.042 and 0.11 μM, respectively); decreases PAH, RVH, and RV peak pressure in a rat model of neonatal hyperoxic lung injury (20 mg/kg per day, s.c.)