The results of 127 left main (LM) coronary angioplasties were reviewed to assess short- and long-term effectiveness. Three major subgroups were considered: (1) elective "protected" (defined as the presence of a patent bypass graft to the left coronary circulation) patients (n = 84); (2) elective "unprotected" patients (n = 33); and (3) acute patients, in whom LM coronary angioplasty was performed in the setting of an acute myocardial infarction (n = 10). Successful LM dilation was achieved in 94% of elective patients and 90% of acute patients. Procedural mortality was 4.3% in elective patients (2.4 and 9.1% in protected and unprotected patients, respectively, p = 0.14) and 50% in the acute subgroup. Long-term follow-up data, available for 98% of patients, revealed actuarial 3-year survival rates of 90 and 36% in elective protected and unprotected subgroups, respectively (p less than 0.0005). In the acute subgroup, 3 patients (30%) were alive at the time of follow-up; all had undergone coronary artery bypass surgery. Thus, although elective angioplasty of an unprotected LM coronary artery is technically feasible, the long-term prognosis of such patients is very poor. LM angioplasty in this subgroup should be reserved for patients in whom surgical revascularization is not an option. In contrast, elective angioplasty of a protected LM coronary artery can be accomplished safely with good long-term results. LM coronary angioplasty for acute myocardial infarction can be effective as a salvage procedure; however, adjunctive coronary bypass surgery is important for long-term survival.