Medical Conditions - Heart Attack

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Heart Attack

(Myocardial Infarction, MI)

The Facts

The heart is one of the largest muscles in the body. The wall of the heart is the muscle that does the pumping, and it is called the myocardium. In a heart attack, this muscle tissue is denied oxygen-carrying blood due to a blocked artery. When the shortage of oxygen gets so bad that many cells die, it’s called infarction. The medical name for a heart attack is an acute myocardial infarction (MI).

Heart attack is directly responsible for about 10% of all deaths in Canada every year. This represents half of all deaths due to coronary artery disease. Although having a heart attack is very serious, the chances of survival are greatly increased if you are able to get to a hospital right away.


Every organ needs oxygen-carrying blood to stay alive, and the myocardium (the muscle that forms the wall of the heart) is no exception. It has its own oxygen supply, via the coronary arteries. In coronary artery disease, fatty deposits (plaques) form in the inner walls of the coronary arteries, narrowing them and reducing blood flow to the heart. This process is called atherosclerosis.

Most heart attacks occur when the atherosclerotic plaque lining an artery ruptures. Blood then forms a clot on the damaged artery, which may partially or completely obstruct blood flow. If the blockage gets severe enough, heart attack symptoms appear, and heart muscle cells may start to die. This is now considered a heart attack.

Rarely, a coronary artery spasm stops blood flow through an apparently healthy coronary artery, causing a heart attack. In most of these cases there’s no identifiable cause.

Symptoms and Complications

Most heart attack victims feel some symptoms in the days leading up to the attack. The most common symptom is angina (chest pain). Chest pain results when the heart muscle is not getting enough oxygen, a condition called ischemia. Angina is likely to get worse or more frequent as the heart attack approaches. Other possible symptoms are extreme fatigue and shortness of breath.

If someone has angina, they may have difficulty distinguishing angina symptoms from heart attack pain. Heart attack symptoms are usually much more severe and longer-lasting (more than 20 minutes) than angina. Heart attack symptoms are relieved only slightly or temporarily by rest or medications used to relieve angina.

Many people report feeling a sense of warning as a heart attack approaches. There can be tightness, pressure, pain, and a "squeezing" feeling in the chest. The pain may also be felt in the back, jaw, shoulder, or arm (especially the left arm). The heart may speed up and beat irregularly. Although chest pain is usually the first symptom, up to 20% of people having a heart attack do not experience chest pain.

These other symptoms may or may not develop:

  • shortness of breath
  • anxiety
  • sweating
  • confusion
  • nausea and vomiting
  • temporary changes in vision
  • lightheadedness

Almost everyone who suffers a heart attack experiences arrhythmias (irregular heartbeats). Some of these irregular heartbeats are harmless, while other types can cause serious problems, even death. One type, ventricular fibrillation (VF), can lead to death in about 5 minutes. The left ventricle, the main pumping chamber of the heart, quivers uselessly instead of delivering blood to the body. The heart does this because of the lack of oxygen delivery.

Not all heart attacks are this severe. In fact, some heart attacks go unnoticed or are shrugged off as heartburn or angina. Distinguishing a heart attack from heartburn is not as easy as you might think – antacids and belching can actually relieve heart attack pain, though it usually returns quickly. Nitroglycerin sprays or pills, often carried by people with angina, may also relieve pain temporarily. However, chest discomfort caused by most heart attacks is not relieved by nitroglycerin. It is important to use your discretion and common sense: if the discomfort feels worse or different than usual, consult your doctor.

Making the Diagnosis

A doctor can tell a lot about a heart with a stethoscope, but the standard test for heart attack is the electrocardiogram (ECG). Electrodes are taped to the chest and the electric signals made by the heart are monitored. Different parts of the ECG wave give information on different parts of the heart and this tells the doctor if there is ongoing damage and where in the heart it may be located.

There’s also a blood test that reveals the presence of a heart attack by looking for a protein that is released when heart cells die. This helps to eliminate the possibility of other conditions that might be confused with a heart attack, such as a blood clot in the lung or pneumonia.

Treatment and Prevention

The first step in heart attack prevention is identifying and reducing risk factors such as smoking, obesity, high cholesterol, and high-fat diets.

Talk to your doctor about personal risk factors and how to make lifestyle changes to reduce the chances of a heart attack, such as:

  • quitting smoking
  • staying physically active and incorporating regular exercise into a daily routine – exercise will help with weight reduction and will lower cholesterol
  • watching your diet – you may need to consult a nutritionist for advice about healthy foods that can help to lower cholesterol

If someone experiences symptoms that might be a heart attack, they should call an ambulance right away. A variety of effective treatments, including thrombolytic ("clot-busting") medications, are available to heart attack victims, but these must be given quickly in order to be effective. 50% of deaths due to heart attack occur within 3 to 4 hours of the beginning of the symptoms. Depending on the hospital, you may be brought directly to the cardiac catheterization laboratory to do an angioplasty, a procedure where a tiny balloon will break open the clot directly. The most important thing you need to do is the reach the hospital as quickly as possible. This will increase the chance of survival.

The hospital’s primary tasks during a heart attack are to stop the damage to heart cells by restoring blood flow, and to deal with complications like ventricular fibrillation. The first medication a person will be given upon entering the hospital is a chewable ASA* (acetylsalicylic acid) tablet. This will help inhibit platelets from forming a blood clot, preventing further blockage of the artery. A range of medications is usually given to reduce the heart’s workload, to dissolve the clot, and to prevent further clotting. An oxygen mask may also be used to increase the level of oxygen in the blood.

A defibrillator is a pair of high-voltage paddles that can deliver an electric shock to the heart. Its purpose is to stop ventricular fibrillation.

After a heart attack, 1 or 2 days of bed rest is usually necessary, but staying bedridden too long can prevent the heart from regaining strength and tends to worsen natural feelings of nervousness or depression. Most people are able to walk a few steps on the third day, but should be careful about straining and lifting heavy objects for a few months.

Medication therapy with ASA or clopidogrel is commonly given to prevent the blood from clotting. Other medications called beta-blockers or ACE inhibitors may also be prescribed. These medications help reduce the heart’s workload and allow easier blood flow from the heart. Cholesterol medications are also important, even if you have "normal" cholesterol levels. Your doctor will recommend these medications depending on your risk of having another heart attack.

If you smoke, it is very important to stop immediately. Heart attack is a complication of coronary artery disease, and it’s best prevented by avoiding the risk factors for coronary artery disease, including smoking.

The early treatment of a heart attack aims to restore blood flow and preserve heart muscle. After a heart attack occurs, you need rehabilitation or post-MI care for the heart to heal and to prevent future attacks. Cardiac rehabilitation programs can usually be planned for in hospital and, depending on the severity of the heart attack, may continue for weeks or months once you return home. Post-MI management includes medication, lifestyle changes, and psychological care.

Finally, following a heart attack, some patients may suffer from depression or experience psychological difficulties related to anxiety or anger. Rehabilitation programs offer help in these areas, providing support and counselling for those who may need it. Although having a heart attack can be a frightening experience, most people can return to their normal activities.


*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.

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