The purpose of this study to determine whether the dual antiplatelet therapy (aspirin and clopidogrel) for 3 months after coronary implantation of zotarolimus-eluting stent is safe in terms of death, myocardial infarction, or stent thrombosis.

Inclusion Criteria:

• Patients with clinically significant de novo coronary artery disease
• Stenting only with Endeavor® stents
• The sum of stent length is less than 60 mm for one lesion. The sum of stent length in multiple lesions does not matter.

Exclusion Criteria:

• Cardiogenic shock
• ST-elevation myocardial infarction within 48 hours of symptom onset
• Prior implantation of drug-eluting stents
• Left ventricular dysfunction (echocardiographic left ventricular ejection fraction < 25%)
• Stenting both branch of bifurcation lesion
• Left main trunk lesion
• Graft vessels
• Patients who have to receive clopidogrel due to other conditions
• Patients who have to receive warfarin, cilostazol or other antiplatelet therapy
• Patient with chronic renal failure (S-Cr > 2.0 mg/dl)
• Hypersensitivity to clopidogrel or aspirin
• Expectant survival less than 1 year
• Women who plan to become pregnant
• Patients with bleeding diathesis (coagulopathy, thrombocytopenia or platelet dysfunction, Gastrointestinal or genitourinary bleeding within the prior 3 months)
• Patients who are actively participating in another drug or device investigational study, which have not completed the primary endpoint follow-up period.