What does QRS complex represent in ECG?

The ECG or electrocardiogram represents the electrical activity in a cardiac cycle. It is an important diagnostic tool to identify any deviations from the normal cardiac activity and heart-related problems.

QRS Complex

The QRS complex is the main spike seen in the standard ECG. It is the most obvious part of the ECG, which is clearly visible.

The QRS complex represents the depolarization of ventricles. It shows the beginning of systole and ventricular contraction.


The QRS complex or wave starts with a small deflection downwards, represented by the point Q. It follows the P wave. After Q, there is a sharp peak, i.e. R and followed by deflection downwards, represented by S. By counting the number of QRS complexes in a minute, we can get the heartbeat rate of a person. The duration of the QRS complex is 80 to 120 ms when the heart is functioning properly.

The other main components of an ECG are:

  • P wave- It represents the depolarization of atria and represents atrial contraction. It precedes the QRS complex
  • T wave- It represents the repolarization of ventricles and the end of the systole. It follows the QRS complex.

The action potential starts at the SA node present in the right atrium and from the atria it passes to the ventricles through the AV node and bundle of His.

Also see: Electrocardiogram (ECG)

The QRS complex has a great significance in clinical diagnosis.

Abnormalities in the QRS complex

  • The widened or prolonged QRS complex indicates the bundle branch block or hyperkalemia.
  • The increased amplitude of R shows cardiac hypertrophy.
  • Abnormality in the Q wave indicates infarction.

This was in brief about the QRS complex and its significance. Get access to all the NEET Questions with explanation, only at BYJU’S.

See More:

Test your Knowledge on ECG!

Leave a Comment

Your Mobile number and Email id will not be published. Required fields are marked *