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 < 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 < 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 < 60% LMCA stenosis entered in the registry (4.5%, p < 0.001). There were 6 in-hospital deaths (14%) in PTCA-LMCA and 4 (21%) in PTCA-OTHER (p = ns). PTCA in the presence of LMCA stenosis, whether the LMCA is the target vessel or not, carries a very high risk, independent of LVEF or the number of vessels dilated, despite the use of PCPB.