Description: • ECG: Graph of the voltage changes that occur during the cardiac cycle. • Readings are taken by electrodes placed on the surface of the body. • Electrodes detect voltage changes caused by the electrical activity of the heart. • P wave = atrial excitation (atrial depolarization). • QRS wave ventricular excitation (ventricular depolarization plus atrial repolarization). • T wave = end of ventricular excitation (ventricular repolarization).