Describe the pathway of electrical activity in the heart during the cardiac cycle.

The wave of excitation originates in the sinoatrial node in the right atrium. From there, it travels through the right and left atria, causing contraction of the atria (atrial systole). It is prevented from travelling further by the atrioventricular node.From the atrioventricular node the wave travels down the septum through the bundle of His and then splits and travels up through the Purkinje fibres, causing contraction of the ventricles (ventricular systole).