Despite improved stent implantation technologies and effective antiplatelet regimens, stent thrombosis has been one of the most important problem in percutaneous coronary intervention. Stent thrombosis is a rare but usually catastrophic event, frequently associated with large MI or death. Stent thrombosis is generally categorized according to the timing of the event as early (0 to 30 days), late (31 days to 1 year), very late (> 1 year). Late and very late stent thrombosis after stent implantation has not yet been adequately characterized, mainly because of its low incidence. And the optimal duration of dual antiplatelet therapy remains uncertain for patients receiving drug-eluting stents.