This is a prospective, single-center study to assess the long- and short-term outcomes of ticagrelor vs clopidogrel in Chinese patients with acute coronary syndrome undergoing percutaneous coronary intervention. Patients will undergo face-to-face interviews, phone calls, or/and chart reviews at 7 days, 1 month, 6 months and 12 months. When 4500 patients have completed the follow-up, an interim analysis will be performed.