What do the sinoatrial node and the atrioventricular node do?

The sinoatrial node and the atrioventricular node controls the Cardiac Cycle- The Sinoatrial node is often called the Pace maker.

The sinoatrial node is located in the wall of the right atrium. The Sinoatrial node emits a wave of electrical activity which reaches both Atria which causes them to contract, the wave of electrical activity is prevented from reaching the ventricles by the atrioventricular septum.

Eventually the electrical activity will reach the Atrioventricular node which is situated between the atria.The Atrioventricular node conveys this along specialised muscle fibres called The Bundle of His.The bundle of his fibres release this electrical activity at the apex of the heart which causes both ventricles to contract at the same time.