Old myocardial infarction of the interventricular septum in a 73 y/o male. There is biventricular hypertrophy and scarring of the septum. Approximately 90% of cases of myocardial infarction are caused by an acute change (e.g. ulceration, fissuring, plaque hemorrhage, rupture) in a previously stable atheromatous plaque in one of the major coronary arteries. The acute change is soon followed by thrombus formation which can occlude the vessel lumen. In about 10% of cases, transmural myocardial infarction occurs in the absence of coronary atherosclerosis. The causes in such cases include coronary artery spasm, emboli from left atrium, paradoxical emboli from the right heart, vegetations in infective endocarditis, and vasculitis etc. Image copyright: pathorama.ch.