Those patients with functionally univentricular hearts are the ones in which surgical repair so as to produce biventricular circulations is deemed impossible, despite the fact that in most instances there are two ventricles within the ventricular mass. Before the era of the Fontan procedure, the typical course of patients with such functionally univentricular arrangements consisted of cardiac failure and death within the first year of life. Despite the advent of effective palliative therapy, ventricular dysfunction remains a significant clinical problem for these patients.