An atheroscloerotic (fat) plaque is a collection of fat which lines the cells of the arterial wall. Cholesterol and fat have a natural liking for arterial walls and often become pulled into the cells of the arterial wall. As the fat increases, deposits, or plaques, of fat are produced which limit the size of the arterial opening. Fat deposits in arteries are referred to as atherosclerosis, and simple hardening and narrowing of the artery is called arteriosclerosis.