Which period of the cardiac cycle is characterized by ventricular relaxation and filling?

The correct answer is characterized by the phase in the cardiac cycle known as ventricular diastole. During this period, the ventricles of the heart are in a state of relaxation following contraction. This relaxation allows the ventricles to fill with blood from the atria due to the pressure difference created by the blood volume returning to the heart.

As ventricular diastole progresses, the atrioventricular (AV) valves open, which facilitates passive filling until the ventricles are sufficiently filled with blood. This is critical for effective cardiac function, as it ensures that there is enough blood available to be ejected during the next contraction (ventricular systole).

In contrast, the other phases focus on different activities of the cardiac cycle such as contraction or filling of the atria. Understanding these dynamics is essential for recognizing how the cardiac cycle maintains an efficient blood flow throughout the body.