Background Despite significant pharmacological and mechanical advancements in PCI,The optimal value of activated clotting time (ACT) during percutaneous coronary intervention (PCI) with unfractionated heparin remains controversial.No data are available on the relation between the ACT at the end of the procedure (final ACT) and the clinical outcomes after transradial PCI.Methods A total of 682 consecutive patients with acute coronary syndrome after transradial Stenting were enrolled into our study,final ACT was available in 658 (96%).All patients were pretreated with aspirin and clopidogrei.After radial sheath insertion,patients received 70 IU/kg unfractionated heparin.Baseline clinical characteristics,procedural success rate,major bleeding and occurrence of major adverse cardiac events (MACE,a composite of death,myocardial infarction or target lesion revascularization) during 30 days and 1 year followup were recorded.