Coronary heart disease is the hardening of arteries from plaque build-up. The hardened arteries restrict blood flow, so your heart cannot receive enough oxygenated blood, especially when it beats quickly during physical exertion or stress. This can cause chest pain and shortness of breath. If an artery becomes completely blocked, a heart attack may occur. Lack of oxygen to your heart during a heart attack causes irreversible damage as the heart muscle dies and is replaced with scar tissue. If damage is severe, the heart may be unable to pump enough blood through the body, a condition called heart failure. Life-threatening irregular heartbeats known as arrhythmias can also occur.