69 Anatomic Considerations in the Functionally Univentricular Heart Robert H Anderson, Diane E Spicer Abstract For many years the “univentricular heart” or “single ventricle” heart has been a subject of contention This is because in hearts that clearly possess two ventricular chambers, one of the two is denied ventricular status The classic example of the lesion thus considered to be univentricular was the arrangement found in the setting of double-inlet left ventricle The artificial nature of such a description was revealed by comparing hearts having double-inlet left ventricles with concordant ventriculoarterial connections and the classic variant of tricuspid atresia At the time when double-inlet left ventricle was considered univentricular, it was generally accepted that tricuspid atresia was a “biventricular” heart Comparison of the variants described above, however, showed that the “infundibular outlet chamber” in double-inlet left ventricle was indistinguishable from the right ventricle in tricuspid atresia Both chambers were examples of incomplete right ventricles lacking their inlet component Comparison with other examples of hearts having either double inlets, or absence of one atrioventricular connection, showed that it was the atrioventricular connection rather than the ventricular mass that was truly univentricular With the advent of the Fontan circulation, it soon became evident that other hearts, which were obviously biventricular, were unable to support the arrangement in which each of the ventricles supplied one or other of the circulations In other words, it was realized that, although hearts with the univentricular atrioventricular connection could never be functionally univentricular, some hearts with biventricular atrioventricular connections might be functionally univentricular The anatomy of the hearts found in patients undergoing functionally univentricular palliation is the subject of the initial section of this chapter, along with the components that follow our anatomic introduction We begin our anatomic assessment by describing in greater detail the evolution of the current concept of the functionally univentricular arrangement We also discuss the anatomic arrangement to be found in the setting of the hypoplastic left heart syndrome, pulmonary atresia with an intact ventricular septum, double-inlet ventricle, absence of one atrioventricular connection, straddling atrioventricular valves, unbalanced atrioventricular septal defect, and complex forms of double-outlet ventricle We conclude the section with a brief analysis of the presumed