Explain Rhythmicity - Properties of a Beating Heart

Not only does the denervated heart continues to beat, it does so remarkably rhythmically. What it means is that the heartbeats are extremely regular. It also means that the time interval between any two consecutive beats is exactly the same. Rhythmicity is conferred on the heart by the conduction system of the heart. The SA node discharges impulses at the fastest rate, the AV node next and the rest of the conduction system does so with the least frequency.

This situation may be understood by imagining a train with more than one engine. If each of the engines is set for running at different speeds, the fastest engine will determine the speed of the train. That is why SA node is the pacemaker of the heart because it determines the pace of the heart. If the fastest engine fails, the second fastest engine will take over and will determine the speed of the train. In the same way, if the SA node fails, the AV node dictates the heartbeats at the slower rate. This orchestra goes on and on rhythmically and coordinated for life.