These dilations, called aneurysms, are prone to rupturing and causing severe internal bleeding. Finally, breaks in the fibrous capsule of fatty plaques can cause ulcerations, leaving underlying fat deposits exposed to the bloodstream. This is ominous because such ulcerations attract platelets from the bloodstream, which clump and release substances that stimulate formation of a blood clot, or thrombus (Figure 3-10D). Enlarging thrombi can quickly occlude arteries, or break off and travel farther down the blood- stream to lodge in a smaller vessel, a phenomenon known as embolism. Complications of atherosclerosis begin as early as the fourth decade of life and increase in frequency with each succeeding decade. Particular consequences of the disease depend on the artery or arteries involved. Blockage of coronary arteries can cause myocardial infarction (heart attack), whereas occlusion or rupture of a cerebral artery can result in a stroke.