In human physiology, the atria facilitate circulation primarily by allowing uninterrupted venous flow to the heart during ventricular systole. By being partially empty and distensible, atria prevent the interruption of venous flow to the heart that would occur during ventricular systole if the veins ended at the inlet valves of the heart. In normal physiologic states, the output of the heart is pulsatile, and the venous inflow to the heart is continuous and non-pulsatile. But without functioning atria, venous flow becomes pulsatile, and the overall circulation rate decreases significantly.