Potent and selective inhibitor of thromboxane (TXA2) synthetase (IC50 = 4 nM). Does not inhibit prostacyclin (PGI2) synthetase, cyclooxygenase or PGE2 isomerase (IC50 > 1 mM). Inhibits platelet aggregation in vitro and arachidonate-induced arterial contraction in vivo.