ECG | Electrocardiogram

ECG Definition

An ECG displays the heart's electrical activity. It reveals the heart's rate and rhythm as well as the details regarding the condition of the heart. They are used to diagnose heart arrhythmias, heart attacks, pacemakers performance and heart failure.

With each heartbeat, an electrical signal moves from the atria to the ventricules. As it travels, the signal causes the heart to contract and pump blood. The process repeats with each heartbeat. An ECG machine records these electrical signals across multiple heart beats and produces an ECG strip that is interpreted by a healthcare professional.

ECG Reading

A normal ECG tracings includes waveform components which indicate electrical events during one heart beat. These waveforms are labeled P, Q, R, S, T and U.

P wave is the first short upward movement of the tracing. It indicates that the atria are contracting, pumping blood into the ventricles.

The QRS complex, normally begins with a downward deflection, Q; a larger upwards deflection, a peak (R); and then a downwards S wave. The QRS complex represents ventricular depolarization and contraction.

The PR interval indicates the transit time for the electrical signal to travel from the sinus node to the ventricles.

T wave is normally a modest upwards waveform representing ventricular repolarization.

Tracing with P Wave, PR Interval, QRS complex and T wave

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ECG Interpretation Tutor

Use our online Workbook to practice your analysis skills and to learn over 40 different types of tracings. After your analysis is completed, our ECG tutor presents an analysis from an electrocardiogram expert.

ECG Interpretation Tutor

Arrhythmia Drills

Using multiple choice questions and answers, users are asked to identify arrhythmia tracings. Digital calipers are available to assist in analyzing each practice strip. Feedback is provided after each response.

Arrhythmia Practice Drills


Our training guide provides information about many types of arrhythmias. For each arrhythmia we provide multiple electrocardiogram tracings. Analysis is provided using a concise summary of the electrocardiogram's key features. Tracing features can be measured using our digital calipers.

Reference Guide

12 Lead ECG Tutorial

New to our website, a presentation on 12 lead ECG prepared by Dr. Michael Mazzini, M.D., Boston University Medical Center.

12 Lead Training

Training - Introduction

The focus of this introductory course is to provide a tutorial about the main features of electrocardiograms along with an analysis method. This method includes assessment of rhythm, calculating heart rate, observing P-wave forms, measurement of EKG intervals and segments and the evaluation of other relevant waves. Practice exercises serve to reinforce the lesson content.

ECG Training


Our website contributors and authors include:

  • Dr. Jon Keroes
  • Dr. Barbara Erikson
  • David Lieberman
  • Diane Wrigley
  • Dr. Michael Mazzini
  • Tom O'Brien
  • The simulation software team at Medical Training and Simulation, LLC


This website is intended for use by medical professionals. All information is for educational purposes only. For medical care please contact a qualified healthcare provider.

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