Final answer:
The pressure of the heart during passive ventricular filling, occurring in ventricular diastole, is low as the heart's chambers are relaxed and blood flows into the ventricles from the atria without active contraction.
Step-by-step explanation:
The pressure of the heart during passive ventricular filling is low. During the cardiac cycle, this occurs in the phase known as ventricular diastole, when the ventricles are relaxed and filling with blood. Due to the relaxation of the ventricular muscles and the opening of atrioventricular valves, the blood flows from the higher pressure in the atria to the lower pressure in the ventricles without the need for atrial contraction. This phase is critical as it allows the ventricles to fill with enough blood to prepare for the next cycle of contraction and ejection of blood during systole.