What Is a Coronary Artery Calcium Score? A coronary artery calcium (CAC) score is a number that reflects how much calcified plaque has built up in the arteries that supply blood to the heart. It is obtained with a quick, non-invasive CT scan of the heart. When cholesterol plaque forms in the artery walls over years, the body often deposits calcium as part of the healing process — so calcium is a visible "fingerprint" of underlying atherosclerosis (hardening of the arteries).