Selective urotensin-II (UT) receptor antagonist (Ki values are 61, 17, 30, 65 and 56 nM at human, monkey, cat, rat and mouse receptors respectively). Inhibits U-II-induced intracellular Ca2+ mobilization (IC50 = 180 nM) and antagonizes the contractile action of U-II in isolated mammalian arteries and aortae (EC50 = 50 - 189 nM).