Coronary artery disease (CAD), also called coronary heart disease (CHD), is a disease in which a waxy substance called plaque builds up inside the coronary arteries. The buildup of plaque occurs over many years. Over time, plaque can harden or rupture (break open). Hardened plaque narrows the coronary arteries and reduces the flow of oxygen-rich blood to the heart. If the plaque ruptures, a blood clot can form on its surface.
Click here for more information. http://www.nhlbi.nih.gov/health/health-topics/topics/cad/