The model's clock runs synchronized to the processing time of required calculations. So, starting off with a timestep of 10 ms, the timestep is increased or decreased until the model runs in actual time.
Each timestep starts with the calculation of cardiac outflow over the current timestep period for right and left circulation separately.
This volume is added to the first capacitance at the left side of the arterial tree. The volume can either stay within this capacitance or flow to the two capacitances in the mid of the arterial tree. The flow velocity is calculated from the pressure difference and the resistance over the connecting tube. The flow that enters into the mid capacitances can either stay within these capacitances or flow to the four capacitances at the far right. The calculation is exactly the same. The outflow of the capacitances at the right can be calculated from the difference of pressure within this capacitance relative to the venous outflow pressure (which in the model is set to 0) increased with possible ICP elevation and the outflow resistance.
At the end of each timestep the model settles on the calculated end situation by Runge-Kutta approximation. The right and left circulation are calculated sequentially. No back flow is allowed when the pressure downstream becomes higher than upstream.
The model cycles from heart beat to heart beat so that at the end of each heart beat the filling time (diastolic period) together with the venous pressure determines the next stroke volume.