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.