Animated Medical Graphics

Heart Attack / Myocardial Infarction

Normal diameter of coronary artery The heart is a mechanical, contractile pump responsible for maintaining blood circulation. It is made of specialized muscle called myocardium and weighs about 10 ounces in the average adult, although many factors affect its ultimate size. This muscle is activated by timed electrical impulses from a part of the heart called the sinoatrial node, the natural pacemaker of the heart. Since the heart is constantly active, it requires an uninterrupted supply of oxygen provided by blood passing through its very own blood vessels - the coronary arteries, represented in the beating heart at the top as irregular, branching lines. The graphic at the right shows the normal width of a coronary artery before it starts branching and forming smaller vessels.

Myocardial infarction, commonly referred to as a heart attack, is death of an area of heart muscle due to a sudden reduction in blood flow relative to the amount of work the heart is doing at the time. Damage from reduced blood flow without any actual heart muscle death results in pain called angina. Blockage in coronary

The most common cause for reduced blood flow initially is coronary atherosclerosis - a gradual build-up over many years of cholesterol plaques, scar tissue, and calcium deposits inside the coronary arteries. Once the opening has been narrowed it is susceptible to sudden blockage by bleeding into and rupture of the cholesterol plaques. A blood clot may then form in the damaged arteries. The animation on the left shows a magnified view of a coronary artery with gradual narrowing followed by rupure and clot formation. Ventricular fibrillation

Once infarction has occurred, the dying area of heart muscle may disturb the normal sequence of electrical impulses by "twitching." If this happens, instead of receiving electrical impulses, the dying area starts sending out impulses to other areas of the heart causing them to contract out of sequence. The heart begins to quiver (ventricular fibrillation, at right) rather than pump rhythmically, thereby further reducing its own blood supply. If this situation is not reversed, death ensues. Another scenario, especially with death of a large part of the heart, is "acute failure", meaning that there is not enough living heart muscle functioning and the heart is simply not strong enough to keep working. At autopsy, the heart may or may not show changes attributable to infarction, depending in part on how long the individual has survived after the incident.

Note: The material provided in this web page is educational in nature and not medical advice. It is meant neither for self-diagnosis nor as a treatment recommendation. If you are concerned about any condition you think you may have, CONSULT YOUR DOCTOR.