 We enrolled patients with stable effort angina who received dual-antiplatelet therapy with both aspirin 100mg and clopidogrel 75mg. We performed PCI 12-24 hours after 300mg loading dose of clopidogrel, or at least 7 days of 75mg clopidogrel treatment after 300mg initial loading dose. We examined platelet adhesiveness, plasma biomarkers for platelet activation such as plasma VWF and ADAMTS13, CD40L, P-Selectin levels, and ADP-induced platelet aggregation using Light transmittance aggregometry LTA and VerifyNow P2Y12 assay system in those patients. We also analyzed the CYP2C19 genetic polymorphism to examine the influence of this genetic variation on the several biomarkers for platelet activation. 