Alternative names


An electrocardiogram (ECG) is a test that records the electrical activity of the heart.

ECG is used to measure the rate and regularity of heartbeats as well as the size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices used to regulate the heart (such as a pacemaker). See also stress test and Holter monitor (24h).

How the test is performed

You are asked to lie down, and electrodes are affixed to each arm and leg and to your chest. This requires cleaning the site and, if necessary, shaving or clipping hair. The standard number of leads attached is 12 to 15 for a diagnostic ECG but may be as few as 3 to 5 for a monitoring procedure.

You are usually required to remain still, and you may be asked to hold your breath for short periods during the procedure. Sometimes this test is performed while you are exercising or under minimal stress to monitor changes in the heart. This type of ECG is often called a stress test.

The results are recorded on graph paper.

How to prepare for the test

Before the ECG, tell your health care provider if you are taking any medications.

There are no restrictions for food or fluids. However, ingestion of cold water immediately before an ECG may produce changes in one of the waveforms recorded (the T wave). Exercise (such as climbing stairs) immediately before an ECG may significantly increase your heart rate.

You may be asked to remove all jewelry and to wear a hospital gown.

In infants and children:
The preparation you can provide for this test depends on your child’s age, previous experience, and level of trust. For general information on how you can prepare your child, see the following topics:

  • Infant test/procedure preparation (birth to 1 year)  
  • Toddler test/procedure preparation (1 to 3 years)  
  • Preschooler test/procedure preparation (3 to 6 years)  
  • Schoolage test/procedure preparation (6 to 12 years)  
  • Adolescent test/procedure preparation (12 to 18 years)

How the test will feel
An ECG is painless. When first applied, the disks may be cold and in rare circumstances, you may develop a localized rash or irritation where the patches are placed.

Why the test is performed
An ECG is very useful in determining whether a person has heart disease. If a person has chest pain or palpitations, an ECG is helpful in determining if the heart is beating normally. If a person is on medications that may affect the heart or if the patient is on a pacemaker, an ECG can readily determine the immediate effects of changes in activity or medication levels. An ECG may be included as part of a routine examination in patients over 40 years old.

Normal Values

  • Heart rate: 50 to 100 beats per minute.  
  • Rhythm: consistent and even.

What abnormal results mean

Abnormal ECG results may indicate the following:

  • Myocardial (cardiac muscle) defect  
  • Enlargement of the heart  
  • Congenital defects  
  • Heart valve disease  
  • Arrhythmias (abnormal rhythms)  
  • Tachycardia (heart rate too fast) or bradycardia (too slow)  
  • Ectopic heartbeat  
  • Coronary artery disease  
  • Inflammation of the heart (myocarditis)  
  • Changes in the amount of electrolytes (chemicals in the blood)  
  • Past heart attack  
  • Present or impending heart attack

Additional conditions under which the test may be performed include the following:

  • Alcoholic cardiomyopathy  
  • Anorexia Nervosa  
  • Aortic dissection  
  • Aortic insufficiency  
  • Aortic stenosis  
  • Atrial fibrillation/flutter  
  • Atrial myxoma; left  
  • Atrial myxoma; right  
  • Atrial septal defect  
  • Cardiac tamponade  
  • Coarctation of the aorta  
  • Complicated alcohol abstinence (delirium tremens)  
  • Coronary artery spasm  
  • Digitalis toxicity  
  • Dilated cardiomyopathy  
  • Drug-induced lupus erythematosus  
  • Familial periodic paralysis  
  • Guillain-Barre  
  • Heart failure  
  • Hyperkalemia  
  • Hypertensive heart disease  
  • Hypertrophic cardiomyopathy  
  • Hypoparathyroidism  
  • Idiopathic cardiomyopathy  
  • Infective endocarditis  
  • Insomnia  
  • Ischemic cardiomyopathy  
  • Left-sided heart failure  
  • Lyme disease  
  • Mitral regurgitation; acute  
  • Mitral regurgitation; chronic  
  • Mitral stenosis  
  • Mitral valve prolapse  
  • Multifocal atrial tachycardia  
  • Narcolepsy  
  • Obstructive sleep apnea  
  • Paroxysmal supraventricular tachycardia  
  • Patent ductus arteriosus  
  • Pericarditis       o Bacterial pericarditis       o Constrictive pericarditis       o Post-MI pericarditis  
  • Peripartum cardiomyopathy  
  • Primary amyloid  
  • Primary hyperaldosteronism  
  • Primary hyperparathyroidism  
  • Primary pulmonary hypertension  
  • Pulmonary embolus  
  • Pulmonary valve stenosis  
  • Restrictive cardiomyopathy  
  • Right-sided heart failure  
  • Sick sinus syndrome  
  • Stable angina  
  • Stroke  
  • Systemic lupus erythematosus  
  • Tetralogy of Fallot  
  • Thyrotoxic periodic paralysis  
  • Transient ischemic attack (TIA)  
  • Transposition of the great vessels  
  • Tricuspid regurgitation  
  • Type 2 diabetes  
  • Unstable angina  
  • Ventricular septal defect  
  • Ventricular tachycardia  
  • Wolff-Parkinson-White syndrome

What the risks are

There are generally no risks. Because this procedure merely monitors the electrical impulses and does not emit electricity, there is no risk of shock.

During an exercise electrocardiogram, some patients experience arrhythmias or heart distress. Equipment for dealing with these occurrences is located in the testing area.

Special considerations

The accuracy of the ECG varies with the condition being tested. Some heart conditions are not detectable all the time, and others may never produce any specific ECG changes.

A person who suspects heart disease or has had a heart attack may need more than one ECG. There is no reason for healthy people to undergo annual testing unless they have inherited risks or a medical condition.

It is important to be relaxed and relatively warm during ECG recording. Any movement, including muscle tremors such as shivering, can alter the tracing.

Johns Hopkins patient information

Last revised: December 8, 2012
by Armen E. Martirosyan, M.D.

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