A heart attack is when low blood flow causes the heart to starve for oxygen. Heart muscle dies or becomes permanently damaged. Your doctor calls this a myocardial infarction.

Most heart attacks are caused by a blood clot that blocks one of the coronary arteries. The coronary arteries bring blood and oxygen to the heart. If the blood flow is blocked, the heart starves for oxygen and heart cells die.

A clot most often forms in a coronary artery that has become narrow because of the build-up of a substance called plaque along the artery walls. (See: atherosclerosis) Sometimes, the plaque cracks and triggers a blood clot to form.

Occasionally, sudden overwhelming stress can trigger a heart attack.

It is difficult to estimate exactly how common heart attacks are because as many as 200,000 to 300,000 people in the United States die each year before medical help is sought. It is estimated that approximately 1 million patients visit the hospital each year with a heart attack. About 1 out of every 5 deaths are due to a heart attack.

Risk factors for heart attack and coronary artery disease include:

• Bad genes (hereditary factors)
• Being male
• Diabetes
• Getting older
• High blood pressure
• Smoking
• Too much fat in your diet
• Unhealthy cholesterol levels, especially high LDL ("bad") cholesterol and low HDL ("good") cholesterol

Higher-than-normal levels of homocysteine, C-reactive protein, and fibrinogen may also increase your risk for a heart attack. Homocysteine is an amino acid. C-reactive protein and fibrinogen are linked to inflammation. Fibrinogen is also involved in blood clotting.

Chest pain is a major symptom of heart attack. However, some people may have little or no chest pain, especially the elderly and those with diabetes. This is called a silent heart attack.

The pain may be felt in only one part of the body or move from your chest to your arms, shoulder, neck, teeth, jaw, belly area, or back.

The pain can be severe or mild. It can feel like:

• Squeezing or heavy pressure
• A tight band around the chest
• Something heavy sitting on your chest
• Bad indigestion

Pain usually lasts longer than 20 minutes. Rest and a medicine called nitroglycerine do not completely relieve the pain of a heart attack.

Other symptoms of a heart attack include:

• Shortness of breath
• Nausea or vomiting
• Anxiety
• Cough
• Fainting
• Lightheadedness - dizziness
• Palpitations (feeling like your heart is beating too fast)
• Sweating, which may be extreme

A heart attack is a medical emergency. If you have symptoms of a heart attack, seek immediate medical help.

The health care provider will perform a physical exam and listen to your chest using a stethoscope. The doctor may hear abnormal sounds in your lungs (called crackles), a heart murmur, or other abnormal sounds.

You may have a rapid pulse. Blood pressure may be normal, high, or low.

Tests to look at your heart include:

• Coronary angiography
• CT scan
• Echocardiography
• Electrocardiogram (ECG) -- once or repeated over several hours
• MRI
• Nuclear ventriculography

Blood tests can help show if you have substances produced by heart tissue damage or a high risk for heart attack. These include:

• Troponin I and troponin T
• CPK and CPK-MB
• Serum myoglobin