Final answer:
About 70-80% of the total blood volume in the ventricles is present during the ventricular diastole phase of the cardiac cycle, when the heart is in a relaxed state and passive filling occurs.
Step-by-step explanation:
Approximately 70-80% of the total blood volume in the ventricle is present during the diastole phase of the cardiac cycle. During this phase, both the atria and ventricles are relaxed, and blood flows from the atria to the ventricles with the help of gravity and the pressure difference. This significant portion of ventricular filling is termed passive filling and occurs before the atrial systole, which contributes the remaining 20-30% of the ventricular filling, also known as the 'atrial kick'.
Therefore, during ventricular diastole, specifically the period of time in the cardiac cycle when both atrioventricular valves (tricuspid and mitral) are open and the semilunar valves (pulmonary and aortic) are closed, the ventricles are loaded with majority of the blood that they will pump out during the subsequent systole. This pre-contraction filling represents the end diastolic volume (EDV), which is an important factor in the calculation of the stroke volume during ventricular systole.