To summarize, changes in venous return will cause a ventricle to move along a single Frank-Starling curve that is defined by the existing conditions of afterload and inotropy. The above analysis shows how changes in ventricular preload lead to changes in stroke volume. In order to do this, is is necessary to describe ventricular function in terms of pressure-volume diagrams. EDV is the maximal volume achieved at the end of filling, and ESV is the minimal volume of the ventricle found at the end of ejection. The ventricular pressure-volume loop is subscribed within the boundaries of the passive and active ventricular pressure curves .
Ventricular filling occurs along the passive curves.
Developed pressure will approach but never exceed the active pressure curve which sets the limit for pressure development at any given preload. When venous return is increased, there is increased filling of the ventricle along its passive pressure curve leading to an increase in end-diastolic volume. If the ventricle now contracts at this increased preload, and afterload is held constant, the ventricle will empty to the same end-systolic volume, thereby increasing its stroke volume. In this way, the normal ventricle is capable of increasing its stroke volume to match any increase in venous return.