To determine the incidence of thromboembolic complications of percutaneous transluminal coronary angioplasty (PTCA) in the setting of recent and acute myocardial infarction, the clinical sequelae and coronary angiographic findings were examined in a series of 13 patients who underwent PTCA either as acute intervention during the infarction or as treatment for recurrent myocardial ischemia that occurred soon after the initial completed infarction. In all cases, the angiographic appearance in the infarct-related artery was that of thrombus in the setting of total or subtotal occlusion. Balloon dilatation without antecedent thrombolytic therapy, was performed in 14 arteries and was successful in establishing reperfusion with reduction of the degree of intraluminal narrowing to less than 50% in all cases. Residual thrombus at the site of inflation was noted in two cases (15%), and embolization was noted in four cases (29%), for an incidence of complication of 44%. In five of six instances in which either residual thrombus or embolization were noted, the initial infarction had occurred greater than 24 h before. In only one of seven cases in which PTCA was used as acute intervention during infarction of less than 4 h duration was the presence of residual thrombus noted after PTCA. Therefore, these findings suggest that thromboembolic complications after PTCA in the setting of recent or acute myocardial infarction are uncommon when the syndrome is less than 4 h duration; however, complications are relatively frequent when infarction has occurred greater than 24 h before. PTCA as a primary intervention in this latter setting should be approached cautiously.