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You have a heart attack when blood can't get to your heart. This happens when one of the vessels that takes blood to your heart is suddenly blocked. If your heart doesn't get the blood it needs, part of it dies. You might be able to tell you're having a heart attack. You might feel severe pain in your chest that can spread down your arms.

If you think you're having a heart attack, call 911 at once. No one will blame you if it's a false alarm. And if it is a heart attack, every minute counts. At the hospital, doctors can run tests and treat you right away. Acting quickly could save your life.¹

• A heart attack is life threatening, but treatment can help you get through it.
• Most treatments work best if you get them quickly. If you think you're having a heart attack, call 911 right away.
• The first thing doctors will do is open the blocked blood vessel. They might do this with drugs. Or a heart specialist might do surgery or an operation to widen your blood vessel. Later, other treatments can help you stay healthy.
• A few changes in your lifestyle can make you feel better after a heart attack. They can also lower your risk of having another heart attack. If you smoke, quit now. Talk to your doctors about getting help.
• You might have to take medication for a long time after a heart attack. Always talk to your doctor before you stop taking your medication or change your dose.

How much do you know about heart attacks? Try our quiz.

Your heart is in the middle of your chest, under your breastbone. It's a muscle that is shaped like a fist. But your heart is different from the muscles in your arms and legs. It works automatically. You don't have to think about making it beat.

Your heart works like a pump. Every time it beats, it pushes blood around your body. Blood carries oxygen and food to your cells. The cells in your body will die if they don't get a constant supply of both.

Your heart is the most important organ in your body. It works harder, and for longer, than any other. If your heart stops working, every other part of your body will die within minutes. To learn more, see How your heart moves blood around your body.

Your heart has thick walls. It's divided into two sides, right and left. Each side has an upper section and a lower section. Doctors call these chambers.

The two chambers on the right side of your heart pump blood to your lungs, where the blood picks up oxygen. Blood then returns to the two chambers on the left side, which pump the blood to the rest of your body, taking oxygen and food to your cells.

The two upper chambers of your heart are called the right atrium and the left atrium. The two larger chambers in the lower part of your heart are called the right ventricle and the left ventricle.²

You don't have to know the medical terms to understand how your heart works. But if you're familiar with them, it might make it easier to understand your doctors when they talk about your heart attack.

Every time your heart beats three things happen:

• The heart relaxes so blood can enter it
• The two upper chambers get smaller, squeezing blood into the two lower chambers
• The two lower chambers get smaller and pump blood out to your lungs and the rest of your body.

Your heart beats around 60 times to 80 times a minute. But it can beat as many as 150 times a minute if you're exercising hard and your body needs more food and oxygen.

To learn more, see How blood moves through your heart and How your heart moves blood around your body.

To do its job, your heart needs its own supply of blood. It gets this from the coronary arteries. These are two major blood vessels that supply the heart with blood that is rich in oxygen.

In most people, the left coronary artery is bigger than the right.

The left coronary artery has two main branches. One is called the left anterior descending artery (or LAD). It supplies most of the blood to the left ventricle, the part of the heart that pumps blood out to your body.

The right coronary artery is smaller. Its branches carry blood to the back of the heart.

Both of these arteries divide into a network of smaller vessels that take blood deeper into the heart muscle.

Your heart needs more oxygen from blood than other muscles do. If you have a heart attack and that supply is cut off, parts of your heart muscle are in danger of dying quickly.

Doctors call a heart attack an acute myocardial infarction (or AMI).

During a heart attack, a blood clot blocks one of the arteries that delivers blood to your heart. When this happens, part of the heart doesn't get enough of the blood and oxygen that it needs.

If the blood supply is cut off for too long, part of the heart will die. The dead part of the heart heals into a scar. This causes permanent damage since heart muscle doesn't grow back.

Heart attacks are always dangerous.

They can cause many different problems for your heart. They can be especially dangerous if, during the heart attack, your heart:

• Beats abnormally
• Can't pump properly. This is called heart failure
• Stops completely. Doctors call this cardiac arrest. To learn more, see Losing consciousness
• Ruptures. This means that the heart muscle tears.
• Stops working properly because its valves aren't working right. Your heart valves keep blood flowing in the right direction.

If you have a heart attack that damages a lot of muscle, you're at a greater risk of serious complications. That's why it's important to get treatment for a heart attack early. The sooner blood and oxygen start flowing to your heart again, the better the chance that your heart will have less damage.

To learn more, see Complications after a heart attack.

Your blood sticks together (or clots) whenever you have an injury, no matter where it is. Blood clots are important because they help keep you from bleeding too much. But when the injury happens inside a coronary artery, the blood clot can lead to a heart attack.

All arteries have a smooth lining. This helps the blood flow through them and keeps it from clotting. But in some people, clumps of fat build up on the lining. (These clumps are called plaques.) Over time, they make the artery narrower, stiffer and less smooth than it should be. Doctors call this condition atherosclerosis. You might also have heard it called hardening of the arteries. Almost everyone who has a heart attack has atherosclerosis in the vessels that take blood to his or her heart (coronary arteries).

Sometimes one of these fatty deposits (plaques) cracks, and a blood clot forms over it just as it would over a cut in the skin. When this clot forms in an artery that is already narrow because it has a plaque in it, the clot might block your artery. We don't know why some plaques suddenly crack while others cause no trouble for years.

We do know that atherosclerosis is very common. It can occur in arteries anywhere in your body. If you have atherosclerosis in your coronary arteries, you have heart disease. You might hear doctors call this ischemic heart disease, coronary artery disease, coronary heart disease or coronary vascular disease. All of the names mean the same thing.

You might have heart disease for many years without knowing it. A heart attack might be the first sign of trouble. Or you might get a type of chest pain called angina. This type of pain is a warning sign of a heart attack. You get angina when not enough blood gets to your heart. It's usually caused by atherosclerosis. But unlike a heart attack, pain from angina usually goes away if you rest.

Doctors call heart attacks by different names, depending on the part of your heart that's affected and how badly it's damaged. To learn more, see Different types of heart attacks.

If you've had a heart attack recently, your life will be on hold for several weeks or longer while your heart recovers and you get over the shock. Many people use this time to make changes in their lifestyles to improve their health.

But you might feel down after your heart attack. Many people who've been ill for a while also feel depressed. Getting treatment for depression might help you cope better with your illness. See Feeling depressed to learn more.

There's a lot you can do to reduce your chance of having another heart attack. If you smoke, now is the time to quit. Eating better, controlling stress and exercising will all help. You can do more to protect yourself by taking the medication your doctor prescribes. Many hospitals and clinics also give workshops on how to care for your heart. To learn more, see Taking care of your heart.

Most heart attacks are caused by fatty deposits (plaques) building up in the arteries that supply the heart. We don't know why this happens to some people and not to others. But we do know that some things make it more likely you'll have heart disease and a heart attack. Doctors call these things risk factors. We've listed the most important below.

• Being male
• Being middle-aged or older
• Having people in your family who've had a heart attack
• Having a low income
• Smoking cigarettes
• Having high cholesterol
• Having high blood pressure
• Being overweight
• Not getting enough exercise
• Having diabetes
• Being under stress

You can't do much about the first three risk factors on our list. And having a low income may be difficult to change. But you and your doctor can work to minimize the danger posed by the others and reduce your chance of having a heart attack.