A stress test, also called an exercise stress test, shows how your heart works during physical activity. Because exercise makes your heart pump harder and faster, an exercise stress test can reveal problems with blood flow within your heart.

A stress test usually involves walking on a treadmill or riding a stationary bike while your heart rhythm, blood pressure and breathing are monitored. Or you'll receive a drug that mimics the effects of exercise.

Your doctor may recommend a stress test if you have signs or symptoms of coronary artery disease or an abnormal heart rhythm (arrhythmia).

A stress test can help:

• Guide treatment decisions
• Determine how well heart treatment is working
• Diagnose the severity of an existing heart condition

Your doctor may recommend a stress test to:

• Diagnose coronary artery disease. Your coronary arteries are the major blood vessels that supply your heart with blood, oxygen and nutrients. Coronary artery disease develops when these arteries become damaged or diseased — usually due to a buildup of deposits containing cholesterol and other substances (plaques).
• Diagnose heart rhythm problems (arrhythmias). Heart arrhythmias occur when the electrical signals that coordinate your heartbeat don't work properly. An arrhythmia can cause your heart to beat too fast, too slowly or irregularly.
• Guide treatment of heart disorders. If you've already been diagnosed with a heart condition, an exercise stress test can help your doctor determine if your current treatment is working. The test results also help your doctor decide on the best treatment for you.
• Check your heart before surgery. Your doctor may use a stress test to determine when you can safely have surgery, such as valve replacement or a heart transplant.

If an exercise stress test doesn't pinpoint the cause of your signs and symptoms, your doctor may recommend a stress test with imaging, such as a nuclear stress test or stress test with an echocardiogram.

A stress test is generally safe. Complications are rare. Possible complications of an exercise stress test are:

• Low blood pressure. Your blood pressure may drop during or immediately after exercise, possibly causing you to feel dizzy or faint. The problem should go away after you stop exercising.
• Abnormal heart rhythms (arrhythmias). Arrhythmias that occur during an exercise stress test usually go away soon after you stop exercising.
• Heart attack (myocardial infarction). Although very rare, it's possible that an exercise stress test could cause a heart attack.

Your doctor will tell you how to prepare for your stress test.

Food and medications

You may be asked not to eat, drink or smoke for a period of time before a stress test. You may need to avoid caffeine the day before and the day of the test.

Ask your doctor if it's safe for you to continue taking all of your prescription and over-the-counter medications before the test. Some medications might interfere with certain stress tests.

If you use an inhaler for asthma or other breathing problems, bring it to the test. Make sure your doctor and the health care team member monitoring your stress test know that you use an inhaler.

Clothing and personal items

Wear or bring comfortable clothes and walking shoes.

A stress test usually takes about an hour, including both prep time and the time it takes to do the actual test. The actual exercise test takes only around 15 minutes. You'll usually walk on a treadmill or pedal a stationary bicycle. If you aren't able to exercise, you'll receive a drug through an IV that mimics the effect of exercise on your heart.

Before a stress test

Your doctor will ask questions about your medical history and how often and at what level of intensity you exercise. This helps determine the amount of exercise that's appropriate for you during the test. Your doctor will also listen to your heart and lungs for any health problems that might affect your test results.

During a stress test

A nurse or technician will place sticky patches (electrodes) on your chest, legs and arms. Body hair may be shaved to help them stick. Wires connect the sensors to a computer, which records your heart's electrical activity. A cuff on your arm checks your blood pressure during the test. You may be asked to breathe into a tube during the test to show how well you're able to breathe during exercise.

You'll probably exercise on a treadmill or stationary bike, starting slowly. As the test continues, the exercise gets more difficult. You can use the railing on the treadmill for balance. Don't hang on tightly, as this may affect the results.

You continue exercising until your heart rate has reached a target level or until you have signs and symptoms that don't allow you to continue. These signs and symptoms may include:

• Moderate to severe chest pain
• Severe shortness of breath
• Abnormally high or low blood pressure
• An abnormal heart rhythm
• Dizziness
• Fatigue
• Certain changes in your electrocardiogram

If you can't exercise during the stress test, you'll be given a drug through an IV that increases blood flow to your heart. You might feel flushed or short of breath, just as you would if you were exercising. You might get a headache.

You and your doctor will discuss your safe limits for exercise. You may stop the test anytime you're too uncomfortable. Your doctor will watch your heart activity and stop the test if there are any concerns.

After a stress test

After you stop exercising, you may be asked to stand still for several seconds and then lie down for a period of time with the monitors in place. Your doctor can watch for any problems as your heart rate and breathing return to normal.

When your exercise stress test is complete, you may return to your normal activities unless your doctor tells you otherwise.

If the information gathered during your exercise stress test shows your heart function to be normal, you may not need any further tests.

However, if the results are normal and your symptoms continue to worsen, your doctor might recommend a nuclear stress test or another stress test that includes an echocardiogram before and after exercise or medications to increase blood flow to your heart. These tests are more accurate and provide more information about your heart function, but they are also more expensive.

If your stress test results suggest that you might have coronary artery disease or show an arrhythmia, your doctor will use the information to develop a treatment plan. You may need additional tests, such as a coronary angiogram.

If you had a stress test to help determine treatment for a heart condition, your doctor will use the results to plan or change your treatment.