Heart disease is a broad term that includes several more specific heart conditions. The most common heart condition in the world is coronary heart disease, which can lead to heart attack and other serious conditions. CHD is the most common type of heart disease. CHD occurs when the coronary arteries, that supply blood to the heart muscle, become hardened and narrowed due to the plaque buildup. The plaque buildup and the narrowing and hardening of the arteries are called atherosclerosis. Plaques are a mixture of fatty substances including cholesterol and other lipids. Blood flow and oxygen supply to the heart can be reduced or even fully blocked with a growing plaque. Plaques may also rupture and cause blood clots that block arteries. CHD can lead to a heart attack. Angina can also occur. Angina is chest pain or discomfort that occurs when the heart muscle is not getting enough blood. Over time, CHD can weaken the heart muscle and lead to heart failure, a serious problem where the heart cannot pump blood the way that it should. Also, irregular heart beats, called arrhythmias, can develop.