Relative contraindications to coronary angioplasty have been large amounts of jeopardized myocardium and poor left ventricular function. To prevent possible hemodynamic collapse after balloon occlusion or acute vessel closure in such high risk patients, a cardiopulumonary bypass system capable of providing up to 6 liters/min output was employed prophylactically. This technique, termed supported angioplasty, results in reductions of preload and afterload and allows prolonged balloon inflations in critical coronary vessels. A National Registry of 14 centers performing elective supplied angioplasty was formed to collate the initial experience with high risk patients. Suggested indications were ejection fraction <25% or a target vessel supplying more than half the myocardium, or both. During 1988, the data from 105 patients (mean age 62 years) undergoing supported angioplasty were entered into the Registry. This group included 20 patients whose disease was deemed too severe to permit bypass surgery and 30 patients who had dilation of their only patent coronary vessel. Seventeen patients had stenosis of the left main coronary artery and 15 underwent dilation of that vessel. Chest pain aid electrocardiographic changes occurred uncommonly despite prolonged balloon inflations. During the trial, there was a progressive change from cutdown insertion to percutaneous insertion of the circulatory support cannulas. The angioplasty success rate was 95% for the 105 patients, who underwent an average of 1.7 dilations per patient. Morbidity was frequent (41 patients), in most cases due to arterial, venous or nerve injury associated with cannula insertion or removal, or both. The overall hospital mortality rate was 7.6%; half of these deaths occurred in patients who were both >75 years of age and had left main coronary artery stenosis. Patients without these two factors had a hospital mortality rate of 2.6%. Symptomatic improvement (lessening of New York Heart Association chest pain classification by at least two classes) occurred in 91% of the patients surviving hospitalization. During the follow-up period of 1 to 12 months, three patients died of cardiac complications. This multicenter experience suggests that supported angioplasty can be safely performed with the expectation of good symptomatic improvement and short-term survival in high risk patients other than elderly individuals with left main coronary artery stenosis. © 1990.