During diastole, what structural changes occur in the ventricles?

During diastole, the ventricles undergo a significant structural change characterized primarily by filling with blood and expanding. This phase of the cardiac cycle is crucial as it allows the heart to refill with blood that will be ejected during the next contraction.

As the heart relaxes, the pressure in the ventricles decreases, allowing blood from the atria to flow into the ventricles. The expansion occurs due to the influx of blood which causes the ventricular walls to stretch. This is vital for ensuring adequate preload, which is important for effective heart function and the overall efficiency of the cardiovascular system.

In contrast, other options do not accurately reflect the physiological events that occur during diastole. For instance, contraction occurs during systole, not diastole, and rigidity and lack of change in the structure of the ventricles do not occur in this phase.