Normally, the walls of an artery are smooth, allowing blood to flow unimpeded. Atherosclerosis is when harmful material collects on the wall of an artery. This material includes fat, cholesterol, and other substances.
Eventually, the material builds up and a plaque is formed, narrowing the artery. When the build-up is severe, a clot could block the vessel completely.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.