Venous return, mean systemic pressure and getting the right answer for the wrong reason

Berger and Takala, in their recent article in this journal (1), adhere to the view that venous return (VR), determines cardiac output (CO) because the heart can only pump out what it receives1. They see VR as driven by mean systemic pressure (Pms), which is opposed by the pressure at the right atrium (Pra)