Encyclopedia / H / Heart Attack

Heart Attack


A heart attack, also known as a myocardial infarction (MI), generally occurs when there is a blockage of blood flow to the heart, resulting in the heart not recieving the oxygen and nutrients it needs.


The human heart basically is a muscle that pumps blood. It has its own blood vessels (the coronary arteries) which nourish it with oxygen and nutrients. In most cases when a heart attack occurs, fatty deposits (composed mostly of cholesterol) have lined the coronary arteries. As these deposits build up, they progressively narrow the arteries and decrease or stop the flow of blood to the heart. When there's a decreased flow of blood to the heart, the heart muscle may be damaged, sometimes permanently, if not treated.

A heart attack most often results when a blood clot forms in a narrowed artery and blocks the flow of blood to the part of the heart muscle supplied by that artery. Doctors call this form of heart attack a coronary thrombosis, coronary occlusion or myocardial infarction.

When a heart attack occurs, the dying part of the heart may trigger electrical activity that causes ventricular fibrillation. Ventricular fibrillation is an uncoordinated twitching that replaces the smooth, measured contractions that cause blood to be pumped to the organs of the body. In many cases, if trained medical professionals are immediately available, they can get the heart beating again by using electrical shock and/or drugs.

If the heart can be kept beating and not too much heart muscle is damaged, small blood vessels may gradually reroute blood around the blocked arteries. This is the heart's way of compensating for the clogged artery. It is called collateral circulation.


Myocardial infarction remains a major cause of morbidity and mortality in the United States. [For a detailed discussion on Causes and Risk Factors see the Health Profile on HEART DISEASE.]


Warning Signals

The key to surviving a heart attack is promptly recognizing the warning signals and getting immediate medical attention. If you feel an uncomfortable pressure, fullness, squeezing or pain in the center of your chest (that may spread to your shoulders, neck or arms) and your discomfort lasts for two minutes or longer, you could be having a heart attack. Sweating, dizziness, fainting, nausea, a feeling of severe indigestion, or shortness of breath may also occur, although not all symptoms do necessarily occur.

When a person has these symptoms, it is natural for him or her to deny what is happening. No one wants to think that he might be having a heart attack. It is important to know that over 300,000 heart attack victims died before reaching the hospital last year, many of them because they refused to take their symptoms seriously.

What should you do if you think you might be having a heart attack? Call your local emergency medical service (EMS) immediately. If the EMS isn't available, get to the hospital Emergency Room as soon as possible.

There is evidence that taking aspirin very early in the course of an MI may help reduce its severity. Thus, taking two aspirin with a small amount of water is advisable.

Know in advance which route from home or work will take you to the hospital the quickest. You might even discuss your possible choices of hospital with your doctor.

Another option is to call your local American Heart Association and ask which recognized emergency medical service and hospitals cover your area. Keep emergency information where you can find it easily and develop a "buddy system" with someone you know.


A physician will take a complete medical history, including a description of your symptoms, a physical exam, perform an electrocardiogram (EKG or ECG) to look for findings suggestive of a heart attack, and order blood tests, including those that check for heart muscle damage. Other studies may also be performed, including a chest x-ray.


Initial treatment may include nitrates - e.g., sublingual (under the tongue) nitroglycerin, oxygen, aspirin and pain medication (e.g., morphine).

The objective of thrombolytic (lysing the thrombus) therapy in acute myocardial infarction is to lyse (dissolve) the coronary thrombus (clot) and allow oxygenated blood to reach the heart muscle as quickly as possible. The goal is that intervention early in the course of infarction will limit infarct size, preserve left ventricular function, prevent pump failure and ultimately, prevent death.

The four thrombolytic agents that have been evaluated extensively in acute infarction are: streptokinase, tissue plasminogen activator (t-PA), reteplase and anistreplase (APSAC). Although there is much debate over which agent to use, the overriding consideration is early adminstration of any one of them.

A number of medical centers now manage acute myocardial infarction with primary angioplasty of the affected coronary artery. Your physician may suggest other treatments as well.


Are there any tests that need to be done to determine if it was a heart attack?

How are the tests performed?

Are there any risks to these tests?

How serious is the condition?

What type of treatment will you be recommending?

Are there any risks or side effects to this treatment?

How effective is the treatment?

Should I take aspirin?

What are the chances of another heart attack?

Are there any preventive measures to prevent this from happening again?

Studies in recent years have shown that taking an aspirin every day may reduce the risk of having a heart attack or a stroke caused by a blood clot forming in an artery. However, it is important that you first consult your doctor before beginning aspirin therapy.

Some studies have shown that the risk of a heart attack during or just after heavy physical exertion is two to six times greater than the risk during less strenuous physical activities or no activity, but regular physical activity diminished the added risk to practically none at all.

Normally sedentary people who try something strenuous like shoveling snow, sprinting to catch a bus, playing tennis or pushing a car out of a snowdrift, may be especially at risk.

Among the cardiovascular benefits of regular exercise are a diminished tendency of blood to form clots, an improved cholesterol profile, more efficient use of oxygen by the muscles, a larger volume of blood pumped with each heartbeat, and during periods of exertion, greater dilation of the arteries, a lower heart rate and lower blood pressure.

Reasonable advice includes the following:

Make sure to discuss any exercise program with your physician first.

Start slow and easy - For the first week or two, exercise at an easy pace for no more than 10 to 20 minutes at a time.

Build up gradually – As a general rule, do not increase either the intensity, frequency or duration of your exercise sessions by more than 10 percent each week.

Exercise often – It is safer to get modest amounts of exercise several times a week than to try making up for days or weeks of inactivity with a single, prolonged workout.

Do not overexert – Beginners should avoid pushing their heart rate higher than 70 percent of its maximum. (Your maximum rate equals roughly 220 minus your age).

Warm up – Begin every workout with a gentle warm-up to boost circulation to the heart muscle. Jog in place, ride a stationary bicycle or do calisthenic exercise for a few minutes. Then stretch to reduce the risk of injury.

Cool down – Rapid muscle movement helps pump blood back to the heart. If you stop exercising abruptly, the heart's blood supply may drop abruptly.

Do not eat and run – During and after a meal, the body sends extra blood to the digestive organs, leaving less blood for the heart and muscles. Try to wait at least two hours after a heavy meal before exercising.

Watch the weather – Blood vessels in the skin and the limbs constrict when it is cold outside, making it more difficult for the heart to pump blood throughout the body. If you exercise outdoors in frigid weather, dress in warm layers and do not push yourself too hard. Working out in hot weather can also threaten the heart, since heavy sweating decreases the total volume of blood, and in turn, the amount flowing to the heart muscle.

Take pollution to heart - Exercising in polluted air increases blood levels of carbon monoxide, which raises the risk of heart attack by replacing oxygen in the blood.