The main function of the heart is to pump bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return round the body.
This can only be done efficiently if the blood returns to the heart (bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return return)
bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return volume is the volume of blood ejected from the heart in one beat.
bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return is the volume of blood ejected from the heart in one minute.
If the amount of blood returning to the heart bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return then the amount ejected will bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return. So VR (bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return) is important because it determines SV (bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return) and Q (bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return)
The is bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return of the Heart.

At rest VR is sufficient to maintain sufficient blood being ejected to supply the bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return for oxygen.

During exercise the pressure of blood in the veins is too bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return to maintain venous return so the volume of blood ejected (SV and Q) bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return. The body therefore needs additional bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return to help push the blood back to the heart to increase VR and therefore SV and Q

There are five mechanisms that help to maintain venous return
1. bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return valves
2. Muscle bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return
3. bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return pump
4. bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return Muscle
5. bloodCardiac outputdecreasesdemandGravityincreaseincreaseslowmechanismsPocketPumpRespiratorySmoothStarlings LawStrokestroke volumevenousvenous return