The SA node possesses a unique property of self excitation, which enables it to act as the pacemaker of heart. It spontaneously generates a wave of contraction which spreads over both the auricles more or less simultaneously along the muscle fibres that fan out from the pacemaker. The pacemaker establishes the basic rhythm at which the heart beats. Thus, if the pacemaker becomes nonfunctional, then the cardiac muscles do not undergo co-ordinated rhythmic movements.