What happens during diastole?

During diastole, the heart relaxes and fills with blood. This phase is crucial because it allows the chambers of the heart, specifically the ventricles, to expand and take in blood from the atria and the lungs. The heart consists of four chambers: two atria and two ventricles. During diastole, the pressure within the heart chambers decreases, causing the atrioventricular (AV) valves to open. This allows blood to flow from the atria into the ventricles without resistance.

This filling is essential for the next phase of the cardiac cycle, systole, where the heart contracts and pumps blood out into the systemic and pulmonary circulation. The process of diastole not only ensures that the heart has enough volume of blood to eject during contraction but also plays a significant role in maintaining adequate blood pressure throughout the cardiovascular system.

The other options do not accurately describe what occurs during diastole, as they either refer to contraction events (which would occur during systole), focus on the role of valves in a way that does not fit the diastolic phase, or introduce unrelated concepts like adrenaline release that do not pertain directly to the mechanics of the heart during diastole.