In a series of 200 cases of unstable angina who have had coronary arteriography carried out, a stenosis of more than 60% of the trunk of the left coronary artery was noted in 40 cases (20%). This sinister site of arteriosclerosis may be suspected in patients presenting with long-standing angina (mean for the group 44 months), an angina which has recently become worse, one which is not responding rapidly to rest and beta-blockers, and in particular one where there has been a previous infarction (50% of cases). Coronary arteriography shows that the lesions were more diffuse and more severe in the group with stenosis of the main trunk. Surgical prognosis becomes worse (31% mortality) because of the risk of vascular complications. Treatment by large doses of Propranolol improves the classically gloomy prognosis of these patients when treated medically.