Diseases can affect any part of the heart. However, the most common is the insidious disease of the coronary arteries called atherosclerosis. When this occurs, plaque, or fatty deposits, develops in the artery walls. Over a period of time, plaque can build up, harden and narrow the arteries, and restrict blood flow to the heart. Clogging in one or more arteries precipitates an attack when the heart's demand for oxygen exceeds the supply.
Diseased arteries are also more susceptible to spasm.
A blood clot can form at the site of a spasm, releasing a chemical that further constricts the artery wall, triggering an attack. When heart muscle is deprived of oxygen long enough, nearby tissue may be damaged. Unlike some tissue, heart muscle does not regenerate. The longer the attack, the more damage to the heart and the greater the likelihood of death. In such an arrhythmia, the heart's ability to pump blood effectively to the brain fails.