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Stress tests make your heart work harder. This allows them to uncover problems that don't show up while you're resting. In unstable angina, the stress test will probably be done when your symptoms are better. This may be at the end of your visit to the emergency room. Or it may be at a later visit to a hospital clinic.

A stress test can help your doctor tell if you have narrowing of the arteries that carry blood to your heart (your coronary arteries). Doctors call this condition coronary artery disease. And the test may show how bad the narrowing is. This can help your doctor decide if you should be offered more tests and maybe surgery.

There are two kinds of stress tests, described below. Your doctor will tell you which kind is best for you.

An exercise stress test shows how much exercise you can do before your heart is put under too much strain. For this test, you walk on a treadmill. Your doctor may speed up the treadmill or make it steeper. At the same time, you have an electrocardiogram (ECG) and your blood pressure is measured.

Your doctor will look at your ECG for changes that happen when your heart isn't getting enough oxygen. You may have bad coronary artery disease if any of the following things happen during this test:

• You get chest pain
• You get short of breath
• Your ECG is abnormal
• Your blood pressure goes down.

In general, the more exercise you can do during the stress test, the more likely your doctor is to say that you have a good outlook.

But the results of your stress test may be normal even if you have coronary artery disease, or they may suggest you have bad disease when you don't.¹ If your doctor suspects a problem, he or she will probably suggest a test called coronary angiography. For more, see Coronary angiography.

Exercise stress testing is very safe. It is always done by well-trained doctors or other professionals. There's a slight risk that this test could bring on a heart attack or a dangerous irregular heartbeat. But this is very rare. Because of this risk, there are guidelines for doctors saying who shouldn't have a stress test.²

If you can't exercise or you have an abnormal ECG while you are resting, your doctor might suggest you have a non-exercise stress test instead. This test doesn't involve any exercise.

For this test, your doctor may give you a drug to make your heart work harder. And he or she may also use a test called an echocardiogram or a scan called a nuclear scan to see how your heart is working. (During a nuclear scan, radioactive chemicals are injected into your blood. The chemicals stick to red blood cells and travel through your bloodstream and heart. Doctors can then use a special scanner see images of your heart and blood vessels.)

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.