Since the pioneering work of Fontan and Baudet, who suggested that a dysfunctional right ventricle could be bypassed by connecting the pulmonary arteries directly to the right atrium in the so-called atriopulmonary anastomosis, much experience has been gained in the field of the functionally univentricular circulation. In view of the continuing need to optimize the fluid dynamics of the connection, research on this topic remains very active. In particular, it is relevant to consider the power dissipated during flow across a connection of this type, due to the low level of the pressure head available for perfusion. The flow to the lungs in this setting is driven only by the low pressure in the caval veins, thus making it essential to minimize the losses of energy in the connection between the terminal part of the venous system and the pulmonary arteries.