Coronary artery disease (CAD) is the most common type of heart disease for both men and women in the United States. It happens when the arteries that supply blood to the heart muscle harden and narrow due to a buildup of cholesterol and plaque on their inner walls. The buildup is called atherosclerosis. As the buildup grows, less blood flows through the arteries, and this prevents the heart muscle from getting enough blood or oxygen. When the heart muscle does not have enough blood or oxygen, chest pain (angina) or a heart attack, can occur.