Fifty-one consecutive patients in whom percutaneous cardiopulmonary bypass support was instituted to enhance the safety of high-risk elective coronary angioplasty were studied. All patients had a low ejection fraction, a large amount of viable myocardium perfused by the target artery(s) or both. Thirty-five men and 16 women, mean age 63 years, with Canadian Cardiovascular Society class III angina (23 patients) or class IV (28 patients) were studied. There was a history of myocardial infarction in 45 (88%), bypass surgery in 14 (27%) and congestive heart failure in 17 (33%). Forty-six (90%) had impaired left ventricular function. Twenty (39%) had an ejection fraction of less than or equal to 25%. Left main stenosis was present in 9 (18%), 3-vessel disease in 48 (94%) and 2-vessel disease in 2 (4%). Twenty (39%) were considered at a prohibitive risk for bypass surgery (14 were turned down for surgery). Bypass was instituted percutaneously with flows ranging from 2 to 5 liters/min (mean 3.6). Angioplasty was successful in 115 of the 117 lesions attempted with the culprit vessel dilated in all. Dilatation of the only remaining vessel was performed in 14 (27%). Inflation times up to 10 minutes were well tolerated. Bypass was discontinued after a mean bypass time of 37 minutes. Hemostasis was achieved by external clamp compression in 50. There were 3 hospital deaths unrelated to bypass. Patient follow-up at 2 to 8 months (mean 4.9) disclosed 1 late death, 31 (66%) asymptomatic patients, 12 (26%) patients in class I and 4 patients (9%) in class II. Thus, this study demonstrates the safety and efficacy of percutaneous bypass support in selected patients undergoing high-risk coronary angioplasty.