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An electrocardiogram (ECG) is one of the simplest and fastest tests used to evaluate the heart. Electrodes are placed at certain locations on the chest, arms and legs. When the electrodes are connected to an ECG machine by lead wires, the electrical activity of the heart is measured, interpreted and printed out. No electricity is sent into the body.


Natural electrical impulses coordinate contractions of the different parts of the heart to keep blood flowing the way it should. An ECG records these impulses to show how fast the heart is beating, the rhythm of the heart beats (steady or irregular), and the strength and timing of the electrical impulses as they move through the different parts of the heart. Changes in an ECG can be a sign of many heart-related conditions.


An ECG is often used:

  • To look for the cause of chest pain
  • To evaluate problems which may be heart-related, such as severe tiredness, shortness of breath, dizziness or fainting
  • To identify irregular heartbeats
  • To help determine the overall health of the heart prior to procedures such as surgery; after treatment for conditions such as a heart attack; and after heart surgery or cardiac catheterization
  • To see how heart medications or an implanted pacemaker are working
  • To get a baseline tracing of the heart's function during a physical exam


An exercise ECG may be done:

  • To assess stress or exercise tolerance for suspected coronary artery disease (blocked arteries in the heart)
  • To determine limits for safe exercise before entering a cardiac rehab program or when recovering from a cardiac event, such as a heart attack or heart surgery
  • To assess heart rhythm and electrical activity during exercise
  • To evaluate heart rate and blood pressure during exercise

What to Expect

An ECG may be done on an outpatient basis or as part of a hospital stay. The patient is asked to remove jewelry and clothing from the waist up and given a gown to wear. A tech may clip or shave small patches of hair to help the electrodes stick to the skin.


During the procedure, the patient lies flat and very still on a table. Electrodes are attached to the chest, arms and legs, and lead wires are attached to the electrodes. The ECG is started and takes just a short time. Once the tracing is complete, a tech disconnects the leads and removes the skin electrodes.


Exercise Electrocardiogram

An exercise ECG is done to assess the heart's response to stress or exercise. In this test, the ECG is recorded while the patient exercises on a treadmill or stationary bike. An ECG tracing is taken at certain points during the test to compare the effects of increasing stress on the heart.


Periodically, the incline and treadmill speed will be increased in order to make exercise more difficult during the test. The patient exercises until reaching a target heart rate or until they are unable to continue due to tiredness, shortness of breath, chest pain or other symptoms. At that point, the patient sits in a chair and their ECG and blood pressure is monitored until they return to normal or near-normal. This may take 10 to 20 minutes.