<P> The time-wise increases and decreases of the heart's blood volume (see Wiggers diagram), are also instructive to follow . The red - line tracing of "Ventricular volume" provides an excellent track of the two periods and four stages of one cardiac cycle . Starting with the Diastole period: the low - volume plateau of "Isovolumic relaxation" stage, followed by a rapid rise and two slower rises, all components of the "Inflow stage"--increasing to the high - volume plateau of the "Isovolumic contraction" stage; (find the label at left side of diagram). Then, the Systole, including the high "Isovolumic contraction" stage to the rapid decrease in blood volume (i.e., the vertical drop of the red - line tracing) which signifies the emptying of the ventricles during the "Ejection" stage of the completed cycle--all equal to one heartbeat . </P> <P> Valve configurations during main stages of the cardiac cycle </P> <Table> <Tr> <Th> Stage </Th> <Th> AV valves * </Th> <Th> Semilunar valves </Th> <Th> Status of ventricles and atria; and blood flow </Th> </Tr> <Tr> <Td> 1 Isovolumic relaxation </Td> <Td> closed </Td> <Td> closed </Td> <Td> semilunar (pulmonary and aortic) valves close at end of ejection stage; blood flow stops . </Td> </Tr> <Tr> <Td> 2a Inflow: (Ventricular filling) </Td> <Td> open </Td> <Td> closed </Td> <Td> ventricles and atria together relax and expand; blood flows to the heart during ventricular and atrial diastole . </Td> </Tr> <Tr> <Td> 2b Inflow: (Ventricular filling with Atrial systole) </Td> <Td> open </Td> <Td> closed </Td> <Td> ventricles relaxed and expanded; atrial contraction (systole) forces blood under pressure into ventricles during ventricular diastole--late . </Td> </Tr> <Tr> <Td> 3 Isovolumic contraction </Td> <Td> closed </Td> <Td> closed </Td> <Td> AV valves close at end of ventricular diastole; blood flow stops; ventricles begin to contract . </Td> </Tr> <Tr> <Td> 4 Ejection: Ventricular ejection </Td> <Td> closed </Td> <Td> open </Td> <Td> ventricles contract (ventricular systole); blood flows from the heart--to the lungs and to rest of body during venticular ejection . </Td> </Tr> </Table> <Tr> <Th> Stage </Th> <Th> AV valves * </Th> <Th> Semilunar valves </Th> <Th> Status of ventricles and atria; and blood flow </Th> </Tr>

Process that causes the last 30 of ventricular volume to fill