Coronary artery disease: Impedance or blockage of one or more arteries that supply blood to the heart, usually due to atherosclerosis (hardening of the arteries). Abbreviated CAD. A major cause of illness and death, CAD begins when hard cholesterol substances (plaques) are deposited within a coronary artery. The plaques in the coronary arteries can lead to the formation of tiny clots that can obstruct the flow of blood to the heart muscle, producing symptoms and signs of CAD, including chest pain (angina pectoris), heart attack (myocardial infarction), and sudden death. Treatment for CAD includes bypass surgery, balloon angioplasty, and the use of stents.