Myocardial infarction. Illustration of a heart with a large area of myocardial infarction (dark area). This occurs when blood flow to part of the heart is interrupted, causing damage to the heart muscle. It results in a heart attack. The outer surface of the heart has small blood vessels which bring blood to and from the heart muscle. An infarction is caused by a blockage in one of these, possibly by a build up of fatty deposits inside a coronary artery, or by a blood clot. Symptoms may include chest pain and shortness of breath. Heart attacks can be fatal but if the damage is limited, treatment is with medication and changes in lifestyle and diet.