Pulmonary arterial hypertension (PAH) is a chronic and progressive disease with a poor prognosis if left untreated. Pathophysiological alterations in this disease lead to vasoconstriction, endothelial and smooth muscle cell proliferation, and in situ thrombosis. Endothelin-1 (one of the most potent vasconstrictors known), has been shown to be increased in PAH, contributing, in part at least, to these abnormalities. Endothelin acts through the binding of two receptors, ETA and ETB. Sitaxentan is a selective ETA endothelin receptor antagonist that has been demonstrated, in several clinical trials, to improve exercise capacity, functional class and hemodynamics. Sitaxentan has a good safety profile, is well tolerated and has a low incidence of liver toxicity.