The most common cause of a significant reduction in the blood supply to the heart is coronary artery disease, or a decrease in the diameter of the arteries supplying the heart muscles. This usually occurs when there is excess lipid or fat deposition inside the walls of these blood vessels, a condition also known as atherosclerosis, usually due to high fat diet.
With constant thickening and hardening of the lipid deposits in the arteries, plaques may form and rupture, which may lead to blood clot formation. These blood clots may further reduce the diameter of an artery or totally block blood flow, leading to cell damage or ischemia.
Other less common causes of myocardial ischemia are coronary artery spasm or sudden contractions of the coronary arteries, sudden decreases in blood volume, infectious diseases and other illnesses such as hypertension that may lead to a decrease in blood supply to the heart.
Risk factors that may lead to ischemic heart disease are advancing age, family history, smoking, lack of exercise, obesity, diabetes and high blood pressure.