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A wave of electrical excitation spreads out from the sinoatrial node across both atria, causing them to contract

A layer of non-conductive tissue (atrioventricular septum) prevents the wave crossing over to the ventricles

This wave of excitation reaches the second group of cells called the atrioventricular node, which lies between the atria

The atrioventriuclar node, after a short delay, conveys a wave of electrical excitation between the ventricles along a series of specialised muscle fibres called Purkyne tissue which collectively make up a structure called the bundle of His

The bundle of his conducts a wave through the atriventriuclar septum to the base of the ventricles, where the bundle brances into smalller fibres of Purkyne fibres