Background The suitable time for treating patients with acute ST elevation myocardial infarction(STEMI)is unclear. This study was to investigate the effects of reperfusion therapy at different late times on patients with acute STEMI,in order to decide the best time for late reperfusion therapy by providing evidence-based treatment in clinical practice. Methods We enrolled 1372 patients with STEMI and receiving selective percutaneous coronary intervention therapy between January 1 st,2010 to December 30 th,2014. According to the time receiving PCI,these patients were divided into 3 groups: