As we described in the previous review,1 double inlet ventricle is usually found with the atrial chambers connected to a dominant left ventricle, less frequently to a dominant right ventricle, and rarely to a solitary and indeterminate ventricle. As we have also discussed in this supplement,2 double inlet to the left ventricle was, for many years, considered the exemplar of so-called “single ventricle”, despite the fact that such patients unequivocally possess one big and one small ventricle. Echocardiographic interrogation has served to resolve this controversy, showing that such patients make up a significant proportion of those having functionally univentricular hearts. Such echocardiographic investigation has also served to resolve similar controversies regarding patients having tricuspid atresia. For some time, it was argued that patients with tricuspid atresia also had “univentricular hearts”,3 but the logic used to underscore this approach was just as flawed as that used to justify the use of “single ventricle” in patients with double inlet atrioventricular connection.4,5 The increasing use of the Fontan procedure has served to demonstrate that these patients, along with many having mitral atresia in the setting of hypoplastic left heart syndrome, also have functionally univentricular arrangements. As we will show in this review, however, the anatomical substrates found in patients with atrioventricular valvar atresia are much more complex than those seen in the setting of double inlet ventricle. This is because atrioventricular valvar atresia can be produced either by absence of one atrioventricular connection, or by presence of an imperforate valvar membranes closing completely one or other of the two normal atrioventricular junctions. This important difference, combined with multiple segmental combinations, produces a bewildering array of potential anatomical substrates, with the complications magnified by the fact that, when one atrioventricular connection is absent, the other atrioventricular junction can be shared between the two ventricles, the so-called uniatrial and biventricular arrangement.6 In our review, we will first describe the anatomical options, before concentrating our attention on the more frequent patterns seen in clinical practice.