Sino-atrial node contracts and transmits electrical impulses throughout atria.
These contract and pump blood into ventricles
Electrical impulse passes to ventricles via atrioventricular node, bundle of His and Purkinje fibres.
Fibres do not contract, but pass impulse to base of ventricles.
Ventricle contract shortly after atria, squeezing blood upwards into arteries
Atria and ventricles relax > atria filll with blood