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Electrocardiogram (EKG) Components and Intervals

An electrocardiogram (EKG, ECG) translates the heart's electrical activity into line tracings on paper. The spikes and dips in the line tracings are called waves.

  • The P wave is a record of the electrical activity through the upper heart chambers (atria).
  • The QRS complex is a record of the movement of electrical impulses through the lower heart chambers (ventricles).
  • The ST segment shows when the ventricle is contracting but no electricity is flowing through it. The ST segment usually appears as a straight, level line between the QRS complex and the T wave.
  • The T wave shows when the lower heart chambers are resetting electrically and preparing for their next muscle contraction.
By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer John M. Miller, MD - Electrophysiology
Last Revised April 4, 2011

WebMD Medical Reference from Healthwise

Last Updated: April 04, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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