Disturbances of myocardial perfusion are mostly due to obstructive coronary atherosclerosis. The shape of the narrowed lumen is polymorphic. The localization of severe stenoses is not influenced by risk factors. Atherosclerotic changes are more frequent in the coronary arteries than in their large branches. There is a good agreement between the localization and the size of the infarct and the poststenotic or postocclusive perfusion area. As a rule there are only few atherosclerotic lesions within samll intramural arteries and arterioles of the myocardium. We could not find a positive correlation between the extent of sclerotic changes in large coronary arteries and arterioles.