During which phase of the cardiac cycle are the atria primarily emptying?

During the cardiac cycle, the atria primarily empty during the systolic phase. This is the period when the ventricles contract and pump blood into the pulmonary artery and aorta, causing a pressure rise in the ventricles. As the ventricles contract, there is a slight increase in atrial pressure which facilitates the emptying of blood from the atria into the ventricles just before the ventricular systole starts.

During this phase, the atrioventricular (AV) valves are open, allowing blood flow from the atria to the ventricles. As the atria contract in the final phase of atrial systole, they push any remaining blood into the ventricles to ensure optimal filling, but the primary act of emptying is occurring concurrently with ventricular contraction. Understanding the mechanics of blood flow during systole helps in appreciating how the heart effectively manages the circulation of blood within the body.