The Electrocardiogram (ECG) : Impulse conduction generates tiny electrical currents in the heart which spread through surrounding tissues to the surface of the body. If electrodes are properly placed on the body surface at specific places, the electric potentials generated by the heart during the transmission of impulse from SA node through conducting system can be recorded. Such a record is called electrocardiogram. The machine used for it is called electro cardio graph.

In mammals the E.C.G. is composed of wave ‘P’, a ‘QRS’ complex and ‘T’ wave. The ‘P’ wave represents atrial depolarization, ‘QRS’ is a wave generated by the spread of the process of excitation through ventricles. T wave is generated as the ventricles recover from the state of depolarization. The significance of ECG is that it tells the defect in the functioning of heart.