Final answer:
During late ventricular diastole, the atrioventricular valves open and passive filling of the ventricles from the atria begins and continues.
Step-by-step explanation:
During late ventricular diastole, the atrioventricular (tricuspid and mitral) valves open, and passive filling of the ventricles from the atria begins and continues. This occurs when the pressure within the ventricles drops below the pressure in the atria. As a result, blood flows from the atria into the ventricles, allowing for ventricular filling.