that development had been normal at least until the eighth week of gestation These lesions, therefore, reflect acquired disease during fetal life It has still to be determined why the heart should develop with either hypoplasia of the left ventricle or an imperforate pulmonary valve As yet, despite multiple efforts, there has been failure to identify any specific genes that might be involved in producing the various lesions Annotated References Anderson RH, Becker AE, Tynan M, et al The univentricular atrioventricular connection: getting to the root of a thorny problem Am J Cardiol 1984;54:822–882 In this review, the members of the European school of nomenclature, supported by the late Robert Freedom, recognized the wisdom of the “morphologic method.” They pointed out that, in hearts with “single ventricles” or “univentricular hearts” it was very rare for the ventricular mass to contain but one chamber In reality, it was the atrioventricular connections that were univentricular in these settings Since then, the European school has based its definitions exclusively on the morphologic method, as explained in the introductory section of this chapter Jacobs ML, Anderson RH Nomenclature of the functionally univentricular heart Cardiol Young 2006;16(suppl 1):3–8 This review showed how, by the addition of a simple adverb, namely functionally, it was possible to defuse all the multiple arguments that continued to surround “univentricular” hearts Almost all hearts described in this fashion have one big and one small ventricle The key point is that only the big ventricle is capable of supporting one or other of the circulations or, in most instances both circulations Hence this arrangement, though not anatomically univentricular, is certainly functionally univentricular Kiraly L, Hubay M, Cook AC, Ho SY, Anderson RH Morphologic features of the uniatrial but biventricular atrioventricular connection J Thorac Cardiovasc Surg 2007;133:229–234 A review of a series of hearts having absence of one atrioventricular connection but with straddling and overriding of the solitary atrioventricular valve It is explained that this produces a uniatrial but biventricular connection Such hearts can exist with absence of either the right or left atrioventricular connection and with right- or left-side ventricular topology This lesion is one variant of the “double-outlet atrium.” Tchervenkov CI, Jacobs JP, Weinberg PM, et al The nomenclature, definition and classification of hypoplastic left heart syndrome Cardiol Young 2006;16:339–368 This extensive review was prepared by the