Diagrammatic presentation of a standard ECG Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart. The P – wave represents the electrical excitation (or depolarisation) of the atria which leads to contraction of both the atria.
The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction. The contraction starts shortly after Q and marks the beginning of the systole.
The T – wave represents the return of the ventricles from excited to normal state (repolarisation). The end of the T – wave marks the end of systole.
