Coronary artery occlusion in heart attack. Illustration of a human heart showing blockage (occlusion) of a coronary artery due to atherosclerosis, a build up of fatty deposits (atheroma, yellow) on the artery wall. The large red vessel is the aorta, the main artery carrying blood from the heart to the body. Two coronary arteries arise from the aorta and supply the heart muscle with oxygen. At right, the blocked area is the anterior inter-ventricular branch of the left coronary artery. Coronary artery disease leads to narrowing of the coronary arteries and abnormal clotting, which blocks the vessel and starves the heart's muscle of blood, causing a heart attack (myocardial infarction).