Basic Facts

  • An electrocardiogram (ECG) is a painless, noninvasive way to help diagnose many common heart problems in people of all ages. 
  • In a standard ECG, 12 stickers, called "leads", are placed on the patient, attached to wires on the ECG machine. Each lead detects the small electrical impulses made by the heart from a different direction, providing a 6 second snapshot of the heart's electrical activity.


If a patient's electrocardiogram is normal, no further testing may be needed. If the results show an abnormality with the heart, the patient may need another ECG or other diagnostic tests, such as ambulatory monitoring or an echocardiogram. Treatment depends on the abnormality and if any signs and symptoms are present from it. 

A healthcare provider will review the information recorded by the ECG machine and look for any problems with the heart, including:

  • Heart rate. Normally, heart rate can be measured by checking your pulse. An ECG may be helpful if your pulse is difficult to feel or too fast or too irregular to count accurately. An ECG can help identify an unusually fast heart rate (tachycardia) or an unusually slow heart rate (bradycardia).
  • Heart rhythm. An ECG can show heart rhythm irregularities (arrhythmias). These conditions sometimes occur naturally, but arrhythmias may also be induced by medications or drugs (beta blockers, over the counter cold and allergy agents, cocaine, amphetamines, etc.)
  • Heart attack. An ECG can show evidence of a previous heart attack or one that's in progress. The patterns on the ECG may indicate which part of your heart has been damaged, as well as the extent of the damage.
  • Inadequate blood and oxygen supply to the heart. An ECG done while you're having symptoms can help determine whether chest pain is caused by reduced blood flow to the heart muscle, such as with the chest pain of unstable angina.
  • Structural abnormalities. An ECG can provide clues about enlargement of the chambers or walls of the heart, heart defects and other heart problems.

Some abnormal ECGs can have major implications. It can indicate anything from a heart attack, to atrial fibrillation, to dangerously high potassium levels in the blood. On the other hand, there are many times when the abnormalities detected are not clinically significant and may have no long-term effects on the heart.