In cases with protected left main stenosis by previous bypass surgery or as an emergency intervention in patients presenting with acute myocardial infarction and cardiogenic shock, percutaneous transluminal coronary angioplasty is performed as an alternative treatment strategy to bypass surgery. A review of 262 left main angioplasties revealed a procedure-related mortality in cases without protection of the left main coronary artery of 9.1% (4/44), in cases with partially protected left main stenosis by collaterals to either left coronary artery of 4.8% (1/21) and 0.5% (1/187) in cases with nonobstructed bypass grafts to either left coronary artery. Coronary angioplasty of an unprotected left main coronary artery, had an unacceptably high procedure-related mortality rate and should therefore not be performed even in cases of emergency intervention. The risk stratification of the procedure can be evaluated by the proposed grading of left main artery protection.