Prospective, two arms, open-labeled, randomized multi-center trial of approximately 2,000 patients enrolled at 19 centers in Korea. Among all patients enrolled in the ZEST (Comparison of the Efficacy of Zotarolimus-Eluting Stent versus Sirolimus-Eluting Stent versus PacliTaxel-Eluting Stent for Coronary Lesions) trial, event-free patients who survived the first 12 months without nonfatal MI or repeat revascularization will be randomized to discontinue clopidogrel therapy at 12 months after DES implantation. All patients will be followed for another 12 months.