The authors report a case of percutaneous dilatation of a coronary artery performed immediately after a mild myocardial infarction and complicated by occlusive thrombosis without dissection, despite a presumably effective anticoagulant treatment. A second dilatation resulted in rapid recanalization of the artery, but recurrent thrombosis developed at the site of dilatation. The thrombotic process was controlled with an intracoronary infusion of urokinase and higher doses of intravenous heparin, but only after a long delay (80 minutes). This case suggests that in similar circumstances one must wait long enough before referring the patient to a surgical unit for emergency aorto-coronary bypass.