Heart disease. Angiogram showing a severe stenosis (narrowing, upper centre) affecting the left coronary artery. The function of the coronary arteries is to supply blood to the heart muscle. Stenoses impair the supply and may lead to angina pectoris (chest pain) or more seriously to a myocardial infarction (heart attack). The obstruction usually builds up from plaques of atheroma (fatty deposits) which can cause athero- sclerosis. Further narrowing may be caused by thrombi (blood clots) formed on the roughened surface of the plaques. A normal blood flow may be restored by using balloon angioplasty in which the artery is stretched by a small balloon.