Ischaemia occurs when there is an inadequate supply of oxygen rich blood to an organ or tissue. This arises as blood vessels become hardened and narrowed because of atherosclerosis, causing obstructed flow of blood through an artery. Narrowing of the insides of arteries that supply the heart muscle leads to reduced blood flow to the heart muscle/tissue. The heart muscle cannot receive sufficient oxygen and other nutrients to do its work, resulting in angina or a heart attack. Ischaemic heart disease that results from poor blood flow to the heart is also referred to as coronary heart disease.