Atheroma. View of the lining of a human aorta showing fatty plaques of atheroma. Atheroma is a mixture of low-density lipoproteins, decaying muscle cells, fibrous tissue, clumps of blood platelets and cholesterol. The plaques narrow the arteries causing the disease atherosclerosis. The condition occurs naturally with ageing but is accelerated by smoking, lack of exercise, high blood pressure, dietary factors and genetic predisposition. Once formed, the deposits cannot be removed. They interfere with blood flow and can trigger the formation of abnormal clots that block arteries. Atherosclerosis is the principal cause of heart attack and stroke.