Current antiplatelet therapy in acute coronary syndrome have a focus on the dual antiplatelet therapy including aspirin and clopidogrel. However, the patient's drug resistance of aspirin and clopidogrel is the important cause of poor clinical prognosis. Therefore, recently, clinical research about the triple antiplatelet therapy including cilostazol is actively conducted. But, clinical research about triple antiplatelet therapy for acute myocardial infarction is inadequate situation, and the ideal duration of triple antiplatelet therapy has been actively discussed. Therefore, we try to evaluate the clinical outcomes of triple antiplatelet therapy in acute myocardial infarction patients undergoing percutaneous intervention with drug eluting stent compared with dual antiplatelet therapy and investigate ideal duration of triple antiplatelet therapy through this research.

Drug-eluting stents (DES) have drastically changed the landscape of percutaneous coronary intervention (PCI), with significant reductions in the angiographic restenosis rate and need for repeated revascularization. However, several studies showed that DES is associated with a higher incidence of in-stent thrombosis compared with bare metal stents. Therefore, the latest guideline for antiplatelet therapy after PCI with DES suggests that the dual antiplatelet therapy (aspirin plus clopidogrel) be administered for at least 12 months.But is it enough for high-risk patients? Some studies showed that as many as 50% of the patients who received PCI did not react positively to aspirin or clopidogrel.Furthermore, there is increased platelet activity in acute coronary syndrome, especially in acute myocardial infarction (AMI). compared with aspirin or clopidogrel.A recent study suggested that cilostazol could ameliorate platelet responsiveness to clopidogrel in patients who underwent primary PCI. Furthermore, some other studies showed that the administration of cilostazol after PCI could significantly lower the incidence of in-stent restenosis. Therefore, the present study is designed to evaluate the safety and efficacy of additional administration of cilostazol with aspirin and clopidogrel in a real-world cardiology practice among patients presenting with AMI who received primary PCI with DES.

Inclusion Criteria: Acute Myocardial Infarction Undergoing Primary percutaneous coronary intervention.

Exclusion Criteria:

1. The patient has a known hypersensitivity or contraindication to any of the following medications: Heparin, Aspirin, Clopidogrel, Cilostazol
2. Uncontrolled hypertension
3. History of bleeding diathesis or known coagulopathy (including heparin-induced thrombocytopenia), or refuses blood transfusions.
4. Baseline hemogram with Hb<10g/dL or PLT count<100,000/μL
5. Patients already taking warfarin, cilostazol or any other type of anti-platelet agents except aspirin and clopidogrel
6. Gastrointestinal or genitourinary bleeding within the prior 3 months, or major surgery within 2 months.
7. Pregnancy