Ventricular filling occurs during

Ventricular filling occurs when ventricles are in diastole (relaxation phase). During joint diastole, atria and ventricles are in a state of diastole. During this phase, blood flows passively from the atria into the ventricles as ventricular pressure is lower than that in atria when atrioventricular valves open. During atrial systole, atria contract while ventricles continue to be in diastole. The contraction of the atria contributes to ventricular filling by pumping an additional 30% of blood into the ventricles.