During the QRS complex.
A graph that documents the electrical activity of the myocardium throughout a cardiac cycle is known as an ECG (electrocardiogram). The P wave, the QRS complex, and the T wave are the three waves that make up an ECG. P waves indicate atrial systole and atrial depolarization. The QRS complex represents the depolarization of the ventricles followed by the activation of the Purkinje fibers. T waves signify the ventricles' repolarization. It indicates ventricular diastole and ventricular myocardial relaxation.
Refer to the image attached for a standard ECG graph.
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