Atherosclerosis. Light micrograph of a section through part of a human coronary artery with atherosclerosis. Atherosclerosis is a build-up of fatty plaques on the walls of arteries. The fibrolipid atheroma plaque is composed of areas of fatty tissue (pale areas in the artery wall) and fibrous tissue (orange, adjacent to the white lumen of the vessel). This narrows the vessel, causing reduced or irregular blood flow. In the coronary vessels this produces angina pectoris (chest pain due to lack of oxygen to the heart muscle). Atherosclerosis also increases the chance of clot formation, which can block a coronary artery resulting in heart attack.