A selective inhibitor of thromboxane A2 synthetase, CV-4151, has the unique property of increasing prostacyclin synthesis in addition to its anti-platelet aggregating effect. Prostacyclin inhibits the growth of smooth muscle cells which is considered to be an underlying mechanism of restenosis occurring after successful coronary angioplasty. A prospective randomized trial was conducted to determine whether CV-4151 could prevent restenosis. Administration was begun greater than or equal to 2 days before angioplasty, and continued until the follow-up study performed between 3 and 6 months after angioplasty. Follow-up angiography was performed in 58 patients (81 segments) taking the active drug and in 27 patients (35 segments) taking the placebo. The incidence of angiographic restenosis was 38.3% in the former group and 31.4% in the latter group. Thus, CV-4151 did not significantly reduce the incidence of restenosis, perhaps due to endothelial denudation after angioplasty preventing an increase of the subendothelial local prostacyclin level.