Between 1 January, 1989, and 28 April, 1990, a total of 888 selective coronary arteriographies were performed at the Institute for Clinical and Experimental Medicine in Prague. Of that number, 58 findings were assessed as at least 50% stenosis of the left main coronary artery (LCA). Having applied exclusion criteria, 50 patients (i.e., 5.63% of all those examined) were entered into a retrospective study. They were 45 men (90.0%) and 5 women (10.0%) with significant cumulation of risk factors for IHD; more than half on them had a history of coronary event. The patients had marked symptomatology--NYHA Class III and higher angina pectoris was present in 96%, a low tolerance of exercise was found in 26 patients undergoing ergometry (average workload of 13 kJ and heart rate of 111/min); exercise testing was invariably evaluated as positive. Coronary angiography regularly revealed multiple coronary artery lesions; the right coronary artery was also involved in 90%; a collateral circulation was present in as little as 34%. The localization of coronary stenoses and the mostly preserved left ventricular mechanical function allowed operative management of IHD in 84% of cases. In the group of patients undergoing surgery, hospital mortality was 4.8%. On long-term follow-up (mean 6.2 months) of the group of patients operated on, 59.9% were free of problem, 31% had NYHA Class II angina pectoris, and there was no improvement at all in one patient only (2.4%). In the group provided conservative therapy (not operated on primarily for severe left ventricular dysfunction), one patient died of recurrent myocardial infarction and cardiogenic shock, 2 have NYHA Class IV angina pectoris, and the remaining subjects continue experiencing NYHA Class III problems.