Illustration of a cross-section through an artery that has become narrowed due to atherosclerosis. A raised yellow plaque is seen in the wall of the artery. This plaque (atheroma) is made of lipids (yellow spheres) and decaying muscle cells encasing crystals of calcium (white and blue). Atheroma plaques are found in people who have a high concentration of certain forms of cholesterol in their bloodstream. Narrowing of the arteries increases the risk of blood clots forming, and is associated with coronary heart disease and stroke.