Understanding the Electrocardiogram (ECG)

Submitted on March 27, 2012
Is Your Heart Quietly Failing? - An ECG can help get to the root of your heart problem easily
Is Your Heart Quietly Failing?

An electrocardiogram or ECG can be described as a simple, non-invasive test, which is used to record the activity and rhythm of your heart. You may be asked to get an ECG done in order to determine the presence of any heart diseases or problems. This test measures -

  • Damage to the heart
  • Heart beat rate
  • Effects of drugs or devices on the heart
  • Position and size of the heart chambers

In case you are suffering from heart problems, you will need to undergo this test once a year. Healthy people do not need a yearly ECG, but a one-time test may be ordered at any time.

Reasons for undergoing an ECG

There could be several reasons why your doctor asks you to undergo an ECG. In most instances, this test will be performed in case you -

  • Have been complaining of chest pain
  • Are experiencing palpitations
  • Are supposed to undergo a surgery shortly
  • Suffered from heart problems in the past
  • Have a family history of heart diseases

Preparing for an ECG

Make sure that you keep your healthcare provider informed about all the medication you take regularly. Some of these drugs may interfere with the results of the ECG. Also, avoid exercising or drinking cold water just before your test or the results may not be accurate.

The ECG Procedure

Just before starting off the procedure, your doctor will ask you to lie down. Several areas on your chest, arms and legs will be sterilized. If required, the hair on those areas may be clipped, before small patches (electrodes) are attached to your skin. There is no fixed number of electrodes used for an ECG.

A machine that converts the electrical signals of your heart into wavy lines is connected to the electrodes. You can see your heart beat in the form of lines on a monitor.

You will be asked to stay still while the procedure is conducted. You may also need to hold your breath at a few points. Being relaxed during the procedure is very important, because even the smallest muscle movement like shivering can alter the results.

There is also a different type of ECG, called the stress test, where the changes in your heart are monitored while you exercise.

After an ECG

Since this is a non-invasive test, you should not feel any discomfort during or after it and can resume your daily activities immediately.

Though rare, there is a possibility of developing a rash where the electrodes were placed, but this is a minor side effect that goes away within a few days.


The wavy lines seen on the monitor are printed on a sheet of paper and are analyzed by a doctor. For a normal result, the reading should be -

  • Heart rate: 60 to 100 beats/ minute
  • Heart rhythm: Even and consistent

In case the reading of the ECG is not normal, you may be suffering from -

  • Accumulation of fluid in the sac around the heart
  • Arrhythmias or irregular heart rhythm
  • Changes in blood sodium or potassium levels
  • Congenital heart defects
  • Heart enlargement
  • Heart muscle damage
  • Low blood supply to the arteries
  • Myocarditis or inflammation of the heart
  • Recent heart attack
  • Swelling in the heart

At times, changes on the ECG test could occur due to heart problems such as -

  • Heart failure
  • Atrial flutter
  • Multifocal atrial tachycardia
  • Wolff-Parkinson-White syndrome
  • Sick sinus syndrome
  • Paroxysmal supraventricular tachycardia

Not all heart conditions show up on an ECG; there are some conditions that never cause specific ECG changes. Therefore, further testing may be required if an ECG does not help diagnose the problem accurately.


  • Ganz L. Electrocardiography. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 54