Atherosclerosis is a disease in which the inside of an artery narrows due to the build up of plaque. Initially, there are generally no symptoms. When severe, it can result in coronary artery disease, stroke, peripheral artery disease, or kidney problems depending on the arteries affected. Symptoms, if they occur, generally do not begin until middle age. The exact cause is not known. Risk factors include abnormal cholesterol levels, high blood pressure, diabetes, smoking, obesity, family history, and an unhealthy diet. Plaque is made up of fat, cholesterol, calcium, and other substances found in the blood. The narrowing of arteries limits the flow of oxygen-rich blood to parts of the body. Diagnosis is based upon a physical exam, electrocardiogram, and exercise stress test, among others. Prevention is generally by eating a healthy diet, exercising, not smoking, and maintaining a normal weight.