2110 patients who received successful dug eluting stent implantation will be enrolled at 21 centers in Korea. Patients meeting inclusion criteria without any exclusion criteria and agree to participate in this trial will be randomized 1:1 to a) triple therapy (Aspirin+Clopidogrel +Cilostazol) or b) dual therapy group (Aspirin+ Clopidogrel +Placebo). All patients will be blindly assigned to cilostazol 100mg (1tablet bid) or matching placebo (1tablet bid) as 1:1 ratio and are prescribed for 1 year.