Electrocardiogram is the recording of the electrical signals of the heart. Electrocardiogram (ECG) recorded from the body surface is known as surface ECG while that recorded with intracardiac electrodes are called electrograms. Standard surface ECG uses four electrodes on the limbs of which one is an indifferent electrode and 6 electrodes on the chest. Various combinations of limb electrodes record 6 ECG leads while chest electrodes record 6 chest leads to make a total of 12 leads in the standard 12 lead ECG. The leads can be recorded in sequence, groups of 3 each or simultaneous 12 leads. Multiple simultaneous leads are useful in the analysis of rhythm disturbances. A long rhythm strip is needed for analysis of arrhythmia.