How does the conduction system of the heart control the systolic phase of the cardiac cycle?

The SA node initiates an impulse which travels across the atria causing them to contract and blood is forced actively into the ventricles. This is called atrial systole. The AV node then delays the impulse allowing the atria to fully finish contracting and emptying. The impulse is then sent along the bundle of HISS and Purkinje fibres, causing the ventricles to contract (ventricular systole) and forcing blood actively out of the heart via the arteries.