Darusentan is a mixture of two isomers R and S. It was investigated whether darusentan was a potent inhibitor of endothelin signaling and function in both large and small arteries. And it was revealed, that R-isomer was inactive, it didn’t have any binding activity to the endothelin receptor of the rat aortic vascular smooth muscle cells (RAVSMs) membrane in comparison with S-isomer. In addition, in isolated endothelium-denuded rat aortic rings, (S)-darusentan inhibited endothelin-induced vascular contractility, but (R)-darusentan had no effect.