Atherosclerotic plaques narrow blood vessels. Plaques result from the accumulation of lipids, lipid-filled macrophages and smooth muscle cells, and extracellular matrix proteins. The left side shows an illustration of a normal artery and one with an atherosclerotic lesion. The right side is a histology section showing a plaque in an artery. Image from OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons.