Medical-surgical aspects of left main coronary artery disease. 
Disease of the left main coronary artery compromises circulation to the major part of the left ventricle and thus threatens massive myocardial infarction and sudden death.  Cardiac catheterization and coronary bypass surgery, in previous reports, have been associated with high mortality and morbidity rates.  We report 50 patients with over 50 per cent narrowing of the left main coronary artery.  The clinical pattern in these patients was variable and a left main coronary artery lesion could not be predicted before coronary angiography.  There was only one death during cardiac catheterization.  One patient died while waiting for elective surgery.  Coronary bypass surgery was performed in 42 patients; one died during surgery.  Forty-one patients are alive at 2 to 39 months follow-up (mean, 19 months).  Thirty-six patients are asymptomatic or have minimal symptoms.  Compared to the prognosis in patients with left main coronary artery stenosis treated medically, coronary bypass surgery performed on urgent basis offers a much better prognosis.  Both coronary angiography and bypass surgery can be performed in these patients with a very low risk.