An electrocardiogram may be used in conjunction with exercise to test the heart’s response to increases and decreases in physical activity. This is called the "exercise tolerance test" or "exercise stress test." During this testing, the same types of electrodes are placed at the same locations on the body and connected to the same type of ECG recording device as for the resting ECG. But for this test, you are usually asked to walk on a treadmill to gradually increase physical activity, or exercise, while the ECG is recorded. If you are unable to tolerate exercise, a medication may be used to simulate the effects of exercise on your heart.

The test may take about 30 minutes, and it is usually recommended that you wear comfortable clothing and shoes. You may be asked to change into an examination gown so it is easier to place the electrodes on your chest. A resting, baseline ECG is recorded before you begin exercising, and your blood pressure will also be recorded via a blood pressure cuff, which will lay in place throughout the testing. This provides both a baseline reading and continuous reading during the test.

You begin exercising at a low level of exertion and then increase the intensity of exercise until a pre-determined end is reached. For example, the healthy individual may exercise to a point of exhaustion, or "maximal" effort. An individual who is being evaluated for heart disease or whose heart treatment is being checked may exercise to any one of the following endpoints as determined by your doctor:

• chest pain is experienced by the patient

• abnormalities are seen on the ECG waveform

• an undesirable change in blood pressure is detected

• a "target" heart rate is achieved, as you are progressing in cardiac rehabilitation or when you have no known heart disease but other factors may prevent exercising to the point of exhaustion

It is important to tell the doctor if you experience any discomfort during the test. Symptoms that should be reported immediately include:

• chest pain, or discomfort in the jaw, arm, or shoulder

• shortness of breath

• dizziness or weakness

• leg cramps