A-192621 is a potent, nonpeptide, orally active and selective endothelin B (ETB) receptor antagonist with an IC50 of 4.5 nM and a Ki of 8.8 nM. The selectivity of A-192621 is 636-fold higher than ETA (IC50 of 4280 nM and Ki of 5600 nM). A-192621 promotes apoptosis in PASMCs. A-192621 alos causes elevation of arterial blood pressure and an elevation in the plasma ET-1 level.