What occurs during the diastole phase of the cardiac cycle?

During the diastole phase of the cardiac cycle, the heart muscle undergoes relaxation, which allows the chambers of the heart—specifically the atria and ventricles—to fill with blood. This relaxation phase is crucial for ensuring that the heart is adequately filled with blood before the next contraction occurs. As the heart muscle relaxes, the pressure within the heart decreases, leading to a drop that allows blood returning from the body (via the veins) and lungs (via the pulmonary veins) to flow into the heart's chambers.

The process also involves the opening of the atrioventricular (AV) valves, which ensures that blood can enter the ventricles without obstruction. This filling phase is vital for maintaining an effective cardiac output, as it sets the stage for the upcoming systolic phase where the heart contracts and pumps blood out to the body and lungs. Thus, the correct answer accurately captures the critical physiological actions occurring during diastole.