The neuroendocrinal system of the heart after construction of a Glenn anastomosis or the Fontan circulation

Many complex cardiac defects produce a functionally single ventricle, in which there is mixing of the systemic and pulmonary circulations. The output from the functionally single ventricle is divided between the two circulations: the proportion going to the systemic and pulmonary vascular beds being determined by the relative resistance to flows within the respective circulations.