Describe the cardiac cycle

Diastole - relaxation of the atria and ventricles means lower pressure within the heart, this causes blood to passively flow through the atria and into ventricles. AV valves are open therefore allowing blood from atria to ventricles but semilunar valves are closed.Systole - during atrial systole the atria contract and force blood into the ventricles. Ventricular systole then occurs where the ventricles contract, AV valves contract , semilunar valves open and blood is pushed out of the ventricles and into the arteries leaving the heart.