Coronary atherosclerosis. Illustration of a human heart showing narrowing of the coronary arteries (red) due to atherosclerosis, a build up of fatty deposits (atheroma, yellow) on an artery wall. This is shown in cutaway view in the anterior descending branch of the left coronary artery (at right). Two coronary arteries arise from the aorta (red, upper left) and supply the heart muscle with oxygen. Blocked or narrowed arteries in coronary artery disease can cause heart attacks. The heart's electrical conduction system (green) includes the sinoatrial and atrioventricular nodes (upper left), and the His and Bachmann bundles, and Purkinje fibres (lower right).