When Fontan and Baudet devised what has become known as the Fontan operation, they understandably assumed that inflow and outflow valves should be included to achieve a pump-like action of the subpulmonary right atrial cavity. Over the following years, however, it became apparent that valves did not function satisfactorily in this situation. Worse, the implanted valves had a tendency to become obstructive, which often lead to critical elevation of the already raised systemic venous pressure. Surgeons gradually realised that the outcomes of surgery designed to create the Fontan circulation were likely to be better without inclusion of valves in the subpulmonary right atrium, and they stopped putting them in.