Atherosclerosis is a disease in which plaque builds up inside your arteries. Arteries are blood vessels that carry oxygen-rich blood to your heart and other parts of your body. Plaque is made up of fat, cholesterol, calcium, and other substances found in the blood.Over time, plaque hardens and narrows your arteries.oronary Heart Disease. Coronary heart disease (CHD), also called coronary artery disease, occurs when plaque builds up in the coronary arteries. These arteries supply oxygen-rich blood to your heart. Plaque narrows the coronary arteries and reduces blood flow to your heart muscle.