The correct option is C Atrial depolarisation An ECG (electrocardiogram) is a test to check the electrical activity of the heart. ECG measures the atrial and ventricular depolarization and repolarization in the form of waves. It comprises of three waves, namely P wave, QRS complex and T wave. P wave in ECG represents atrial depolarization. QRS complex represents ventricular depolarization. T wave represents ventricular repolarization.