Coronary artery disease (CAD) is the most common type of heart disease. CAD is caused by plaque buildup in the wall of the arteries that supply blood to the heart. This causes the arteries to become hardened and narrow which, over time, can weaken the heart muscle. You may not know you have coronary artery disease since you may not have symptoms at first. The buildup of plaque in your arteries happens slowly over many years. But as your arteries narrow, you may notice mild symptoms. The most common symptoms are chest pain or shortness of breath. Some people may not know they have CAD until they have a heart attack. You can have an increased risk for CAD if you have high blood pressure, high cholesterol, diabetes, a family history of CAD, smoke or are overweight.