ECG is Electrocardiogram. This represents electrical activity of the heart in graph format and is recorded by a machine known as Electro- cardiograph. This graph is obtained by connecting the patient to the machine by means of three limb leads and six chest leads. The ECG shows many peaks and each peak is denoted by an alphabet 'P' to 'T' referred as Waves. P wave marks the beginning of ECG and it denotes the conduction by Sino- Atrial node .P wave is followed by P-Q interval and this represents conduction through S.A node to AV node and rest of the conducting tissues.