Percutaneous coronary intervention is not successful in all patients whose acute myocardial infarction is controlled with primary angioplasty, and, after an initial successful procedure, reperfusion is not always sustained due to subacute (stent) thrombosis. In a studied population that had acute myocardial infarction, failed mechanical reperfusion occurred in 108 patients (6.9%). Killip's class >I at admission, a left anterior descending artery as the infarct-related vessel, or a preprocedural Thrombolysis In Myocardial Infarction grade 0 or 1 flow was an independent predictor of failed reperfusion. Outcome after successful early and sustained mechanical reperfusion is excellent. Failure of the initial procedure and reocclusion of the infarct-related vessel are important determinants of adverse outcome.