Despite the clarity of the sequential segmential segmental approach to complex congenital heart malformations, the classification of hearts with overriding arterial valves remains contentious. A series of 67 hearts, all with overriding arterial valves, has therefore been studied in an attempt to provide clear and unambiguous criteria for their classification. There were 51 hearts with an overriding aortic valve, 13 hearts with an overriding pulmonary valve and 3 specimens with overriding of both valves. In each of these categories the degree of override and the underlying morphology varied considerably. The options to classify these hearts are limited. Using the "50 per cent rule" as a device to catalogue the type of connexion - irrespective of the morphology - all hearts were described in unambiguous fashion. A comparison with synonyms, as frequently used for purposes of classification, revealed that the latter are often insufficient properly to classify the basic abnormality. By classifying the type of connexion and describing the morphology separately, no basic problem remains in distinguishing between hearts with double outlet right ventricle and subpulmonary ventricular septal defect and hearts with the morphology of Fallot's tetralogy with an aorta almost exclusively arising from the right ventricle. Similarly, the classification of hearts with complete transposition and subpulmonary defect in the setting of the so-called Taussig-Bing heart is brought back to its proper perspective. Proper and consistent application of the sequential segmental approach leaves no room for ambiguity, even in complicated hearts with overriding arterial valves.