<P> During early ventricular diastole, pressure in the two ventricles begins to drop from the peak reached during systole . When pressure in the left ventricle falls below that in the left atrium the mitral valve opens due to a negative pressure differential (suction) between the two chambers, causing blood in the atrium (accumulated during atrial diastole) to flow into the ventricle (see graphic at top). Likewise, the same phenomenon runs simultaneously in the right ventricle and right atrium through the tricuspid valve . </P> <P> The ventricular filling flow (or flow from the atria into the ventricles) has an early (E) diastolic component caused by ventricular suction, and then a late one created by atrial systole (A). The E / A ratio is used as a diagnostic measure as its diminishment indicates probable diastolic dysfunction . </P> <P> Early diastole is a suction mechanism between the atrial and ventricular chambers . Then, in late ventricular diastole, the two atrial chambers contract (atrial systole), causing blood pressure in both atria to increase and forcing additional blood flow into the ventricles . This beginning of the atrial systole is known as the atrial kick--see Wiggers diagram . The atrial kick does not supply the larger amount of flow (during the cardiac cycle) as about 80 per cent of the collected blood volume flows into the ventricles during the active suction period . </P> <P> At the beginning of the cardiac cycle, all four chambers of the heart--two atria and two ventricles--are in relaxation and dilation, or diastole . The atria are filling with separate blood volumes returning to the right atrium (from the vena cavae) and to the left atrium (from the lungs). After chamber and back pressures equalize, the mitral and tricuspid valves open, and the' return' blood flows are passed through the atria into the ventricles . When the ventricles have completed most of their filling, the atria begin to contract (atrial systole), forcing blood under pressure into the ventricles . Now the ventricles start to contract, and as pressures within the ventricles rise, the mitral and tricuspid valves are closed . </P>

About 80 of blood is passed from the atria to ventricles by