During which phase are the atrioventricular and aortic valves closed?

During diastole, the heart muscle relaxes, allowing the chambers of the heart to fill with blood. During this phase, both the atrioventricular (AV) valves, which separate the atria from the ventricles, and the aortic valves, which lead from the ventricles to the aorta, are closed. This closure prevents backflow of blood into the heart while it fills, ensuring that blood moves efficiently from the atria to the ventricles and is then properly ejected into the systemic circulation during the next contraction.

In contrast, during systole, the ventricles contract and the AV valves are closed to prevent blood from flowing back into the atria. Meanwhile, the aortic valves are opened to allow blood to flow from the heart into the aorta. Atrial systole is a phase of the cardiac cycle where the atria contract, further filling the ventricles, but during this moment, the AV valves are open to facilitate that flow. The term "cardiac output phase" is not standard in the context of the phases of the cardiac cycle and does not accurately describe the closing of the valves; it generally refers to the overall function of the heart during its pumping action.