Cilostamide is a selective and potent PDE3 inhibitor, with IC50s of 27 nM and 50 nM for PDE3A and PDE3B, respectively, and has antithrombotic and anti-intimal hyperplastic activity. Cilostamide weakly inhibits PDE2, PDE4, PDE5, PDE7, and PDE1, with IC50s of 12.5, 88.8, 15.2, 22.0 and > 300 μM, respectively. Cilostamide potently inhibits thrombin-induced platelet aggregation (IC50, 1.1 μM).