Describe how the rhythmicity of the heart is established and maintained with respect to the different stages in the cardiac cycle (6 marks)

The Sinoatrial Node (SAN) generates the wave of excitation/ Action potential (AP).

The AP spreads across the atrial walls, stimulating the myocardial cells to contract This initiates the atrial systole.

The AP is then transmitted to the Atrioventricular Node (AVN).

Here it is delayed.

Once Atrial systole has finished the AP is conducted down the purkinje fibres/ bundle of His.

when it reaches the apex/base of the Heart it spreads across the ventricular walls.

This stimulates the myocardial cells in this region to contract.

This initiates the ventricular systole.