Atherosclerosis. Illustration of a cross-section through an artery narrowed by atherosclerosis. Fat build-up (yellow) has narrowed the lumen (channel) of the artery thus restricting the blood flow. Red blood cells (red, disc shaped), yellow fatty particles and white blood cells (blue) are seen flowing through the artery. Narrowed arteries such arteries such as this are found most often in people who have a high concentration of cholesterol in their bloodstream. Narrowing of the arteries increases the risk of blood clots forming, and is associated with coronary heart disease and strokes.