To assess the outcome of PTCA in circulatory supported patients with left main coronary artery (LMCA) stenosis, the National Registry of Elective Supported Angioplasty data bank was searched. Patients entered in the registry were considered high-risk PTCA and the PTCA was performed using percutaneous cardiopulmonary bypass (PCPB). Criteria for high risk was left ventricular ejection fraction less than or equal to 25% or a target lesion supplying greater than or equal to 50% of functioning myocardium. Of 455 patients entered in the registry, 61 (13.3%) had LMCA stenosis greater than or equal to 60%. There were 42 patients in whom the PTCA target vessel was the LMCA (PTCA-LMCA) and 19 in whom it was vessel(s) other than the LMCA (PTCA-OTHER). The mean age was similar in the 2 groups (65 +/- 10 vs. 68 +/- 9 yrs, p = ns). The left ventricular ejection fraction (LVEF) was higher in PTCA-LMCA than in PTCA-other (38 +/- 16% vs. 27 +/- 16%, p less than 0.05). The number of vessels dilated/patient was higher in PTCA-LMCA than in PTCA-OTHER (2.1 +/- 1.0 vs. 1.1 +/- 0.3, p less than 0.001). There were a total of 10 in-hospital deaths (16%) in patients with LMCA greater than or equal to 60% stenosis. This exceeds the mortality of the patients with less than 60% LMCA stenosis entered in the registry (4.5%, p less than 0.001). There were 6 in-hospital deaths (14%) in PTCA-LMCA and 4 (21%) in PTCA-OTHER (p = ns).(ABSTRACT TRUNCATED AT 250 WORDS)