A heart attack (myocardial infarction) occurs when heart muscle is damaged or destroyed because it does not get enough oxygen-rich blood to sustain life. Just as the heart supplies oxygen and nutrients to other parts of the body, blood vessels called coronary arteries supply needed blood to the heart. If one or more coronary arteries or the blood vessels that feed blood into the major arteries are blocked or narrowed, the heart muscle is deprived of oxygen. If the oxygen supply is cut off for more than several minutes, the heart cells suffer permanent injury or death.

The medical term for heart attack is myocardial (meaning "heart muscle") infarction (an area of dead heart tissue is an "infarct").

The heart has four major arteries. Blood is pumped out through the largest of these arteries, the aorta, which circulates it through the body. The pulmonary artery supplies blood to the lungs. The right and left coronary arteries bring oxygen rich blood to the heart itself.

Myocardial Infarction is not the same as cardiac arrest, or sudden cardiac death (SCD)!

SCD is caused by a deadly heart rhythm disorder (arrhythmia) called ventricular fibrillation (VF).

Heart attack survivors often are at risk for sudden cardiac arrest. This is because a heart attack can damage areas of heart muscle that affect the electrical conduction system of the heart. This system is responsible for sending the signals that tell the heart when to contract, and regulate the heart's steady rhythmic beat.

In VF, the electrical signals that trigger the heartbeat become very fast and chaotic in the lower chambers of the heart. The heart no longer can pump blood to the brain or body. Without immediate emergency help, the heart cannot recover. Heart disease is the leading cause of death in the U.S. About half of all deaths from heart disease are due to sudden cardiac arrest, the inevitable result of VF.

What Causes a Heart Attack?

Heart attacks most often result from coronary heart disease (also called coronary artery disease or ischemic heart disease). The most common cause is atherosclerosis ("hardening of the arteries"), a build-up of fatty deposits called plaque. Over time, plaque clogs and narrows the arteries and other blood vessels, and slows or blocks the flow of blood to the heart and elsewhere. Sometimes, the surface of plaques can rupture or tear, which can cause blood clots to form that block the arteries. A complete or near-complete blockage of the coronary arteries results in a heart attack.

Signs and Symptoms

The signs and symptoms of a heart attack vary from person to person, but they usually are not as obvious and dramatic as people imagine. Many heart attacks start slowly, usually with a feeling of pain or discomfort in the chest that lasts more than a few minutes, or goes away and returns. Pain from a heart attack generally lasts for more than 30 minutes, and may continue for several hours. The longer the pain lasts, the greater the risk of muscle damages. Chest pain due to a reduced blood supply to the heart is called angina. It may be a warning signal of a heart attack.

People may feel different symptoms during a heart attack or MI - and some people feel no unusual symptoms. Classic heart attack symptoms are described as:

An intense aching in the left side or center of the chest
Sometimes, the pain radiates into the neck, back, arms or jaw
A feeling of extreme pressure, fullness, or tightness in the chest
Nausea, dizziness, weakness, shortness of breath, or a cold sweat also can be experienced
Not everyone experiences acute chest pain and some may have a combination of symptoms. Other heart attack survivors report a vague feeling that their heart or health is "not quite right." There may be only a slight discomfort. About one-quarter of all heart attacks occur without producing any noticeable warning signs. These "silent" heart attacks may go undiscovered until they show up during routine heart tests such as an electrocardiogram (ECG).

If you think you may be having a heart attack, even if the symptoms are mild, seek medical attention immediately.

When in doubt, it is best to call your doctor, go to the nearest emergency room, or call as soon as your symptoms develop.

The sooner emergency treatment is provided, the greater the chance that permanent damage to the heart muscle can be avoided.

When administered shortly after the onset of a heart attack, clot-busting drugs (called thrombolytic therapy), angioplasty or other treatments may be able to open blocked coronary arteries and restore the normal supply of blood and oxygen to the heart. The more time that goes by, the more harm is done to the heart muscle.

What's your Ejection Fraction (EF)?

The proportion, or fraction, of blood pumped out of your heart with each beat is called the ejection fraction, or EF. A normal heart pumps out a little more than half the heart's volume of blood with each beat. A normal EF is 55 percent or higher. Your doctor can order simple, painless tests such as an echocardiogram which creates a moving picture of your heart using harmless soundwaves, or a nuclear medicine test that show's how well your heart is pumping. If your EF is abnormally low, you may need further tests to see if you have an abnormal heart rhythm.

Many people who have survived a heart attack can benefit from an implantable cardiac defibrillator (ICD), a pacemaker-like device that treats ventricular fibrillation (VF), the deadly heart rhythm that causes sudden cardiac death. Recently, several large clinical studies were conducted to see if ICDs could prevent sudden cardiac death in people whose heart muscle - and its pumping ability -is damaged by a heart attack. In the studies, survival rates were significantly greater for people with ICDs than for people who received traditional medical care.

An ICD is a pacemaker-like device implanted under the skin. Wires called "leads" are placed in the heart to monitor the heart rate. When the device detects a potentially deadly heart rhythm disorder (arrhythmia), the ICD delivers a controlled, electric shock to restore the heart's normal rhythm. This device was implanted in vice-president Dick Cheney to monitor his heart rhythm and provide immediate treatment if his heart rate gets too slow or too fast.

Do you know your EF? If you don't, ask your doctor. It could save your life.
If you have had a heart attack, take our quiz to learn if you may be at high risk for sudden cardiac arrest.

For more information about heart attack and related disorders, go to:

The Normal Heart
Symptoms of heart disease
Treatments for heart disease
Risk Factors and Prevention
Sudden Cardiac Death (SCD)