A relationship was studied between the intensity of smoking and changes revealed in the coronary arteries by coronarography in 498 patients with ischemic heart disease. Marked atherosclerosis was found in 94% of "regular" smokers and in 69% of the persons who did not smoke or smoked only a little. A particularly clear connection between the intensity of smoking and affection of the coronary arteries was registered in patients with ischemic heart disease under the age of 40. All of them had grades III and IV stenosis of the coronary arteries. The results discussed confirm that smoking is a serious "risk factor" of the development of ischemic heart disease, especially in young individuals.