East Asian patients will be required optimal dose of newer P2Y12 inhibitor (ticagrelor) to determine the safer treatment and better outcome. Whether low dose of ticagrelorI is more adequate for clinical practice in Korea is unclear. Therefore, the investigators aim to evaluate efficacy and safety of low dose of ticagrelor in Acute Myocardial Infarction (AMI) undergoing percutaneous coronary intervention(PCI).

In recent years, newer oral P2Y12 receptor blocker (ticagrelor) has been strong recommendations for management of patients with AMI undergoing (PCI). This drug provided more profound inhibitory effects than clopidogrel, which could lead to marked reduction in ischemic events, with relatively increase in bleeding complication, specific to low body weight, especially in women and East Asian patients.

Inclusion Criteria:

• Patients present with acute myocardial infarction undergoing PCI.
• Patients receiving ticagrelor; Male or female gender; Age 20-75 years.
• Patients provide written informed consent prior to enrollment.

Exclusion Criteria:

• Low body weight (<60kg).
• History of hemorrhagic stroke.
• History of upper gastrointestinal bleeding in recent 6 months.
• Bleeding tendency.
• Thrombocytopenia defined by platelet < 100,000/ml.
• Anemia defined by hemoglobin < 10 g/dl.
• Renal dysfunction defined as serum creatinine > 2.5 mg/dl.
• Severe hepatic dysfunction defined as serum transaminase > 3 times normal limit.
• Known severe chronic obstructive pulmonary disease or bradycardia (sick sinus syndrome (SSS) or high degree AV block without pacemaker protection).
• Current treatment with drugs interfering with CYP3A4 metabolism (to avoid interaction with Ticagrelor): Ketoconazole, itraconazole, voriconazole, clarithromycin, nefazodone, ritonavir, saquinavir, nelfinavir, indinavir, atazanavir, and telithromycin.