Ischemic heart disease, also known as coronary artery disease, occurs when the heart's blood supply is reduced due to narrowing or blockage of the coronary arteries. This decrease in blood flow, often caused by the buildup of fatty deposits or plaques, leads to a lack of oxygen and nutrients to the heart muscle, which can result in chest pain (angina), shortness of breath, or heart attacks. Over time, this condition can weaken the heart muscle, leading to heart failure or other complications.