The heart is modeled as a simple volume pump. It fills depending on venous pressure over the duration of diastole. In the model the right side of the heart may fill at a different speed than the left side depending on venous preload. Leaving the model to it, the total volume will spread over the right and left circulation automatically, until the filling of the right and left side of the heart are balanced. For instance, in the model change the capacitance of the venous system (lower slider in the resistances and capacitances box) and see how it takes time for the volume to spread so that the stroke volumes of the right and left side of the heart become equal again.
The residual volume of the right and left side of the heart is arbitrarily set to 50 ml so that some volume will always stay behind after contraction. The stroke volume is modeled as the cardiac volume minus the residual volume at the end of diastole times the ejection fraction. Normally, the ejection fraction is set to 1.0 but it is decreased to 0.7 during the two scenario's simulating left or right decompensation.
The outflow is modeled as a sine function spanning the time of systole with the stroke volume as total surface below the curve.