We reviewed the records of 402 patients undergoing percutaneous transluminal coronary angioplasty to identify factors predicting an ischemic event with arterial disruption during an otherwise uncomplicated angioplasty. Major dissection of the coronary arteries without immediate occlusion was found in 25 patients, who exhibited 28 dissected lesions. Dissections were classified into 2 types: those producing a continuous extraluminal and parallel filling tract, and those with a continuous parallel filling tract extending into and compromising the lumen. Ischemic complications (defined as myocardial infarction, the need for repeat angioplasty, or coronary arterial bypass surgery) occurred in 6 patients (24%) within 24 hours of the completion of the procedure. The remaining 19 patients had an uncomplicated hospital course. Acute ischemic complications following dissection correlated with the percentage of luminal compromise 50 +/- 0% in those with complications as opposed to 17 +/- 21% in those without: P less than 0.001) and the development of dissection producing a filling tract which compromised at least half the lumen (100% in those with complications versus 9.1% in those without: P less than 0.001). There was a trend towards an increase in ischemic complications in patients with proximal and eccentric lesions. We conclude that patients who develop dissections which produce significant luminal compromise after an otherwise uncomplicated angioplasty are at a high risk of developing an acute ischemic complication within 24 hours of the procedure.