Acute myocardial infarction, treatment with vitamin K antagonists and the use of antiGP2b3a before PCI. All patients are pre-treated with clopidogrel and aspirin. Non-response to aspirin or clopidogrel is determined according to the result of the VerifyNow assay (cut off : < 15 % for P2Y12 and > 550 ARU for aspirin). The primary end point is the occurrence of definite or probable stent thrombosis (ARC definition) and the secondary end-points include global and cardio-vascular mortality, non fatal myocardial infarction and major bleeding. A clinical evaluation is scheduled at discharge and by telephone contact at one month and one year.