Ventricular dysfunction is frequently encountered in Fontan patients. Cardiologists and cardiac surgeons have, therefore, mainly focused on preservation of cardiac function, limiting the early volume overload as much as possible both in magnitude and duration. This resulted in improved cardiac function but, in some patients, also in poor pulmonary artery (PA) growth which in turn resulted in a poor final Fontan circuit. The volume requirements for optimal growth and development of the ventricle and the lungs are different and divergent. Avoiding overload of the ventricle is important, but excessive protection from volume overload may not be necessary and may result in PA hypoplasia, which in turn will severely affect the Fontan circuit.