Hearts which, at first sight, seem to have a solitary chamber within their ventricular mass have long been the subject of controversy. As difficult as it is to manage these cardiac malformations medically and surgically, it has been at least as challenging, to date, merely to describe and classify them. Even the most commonly used terms, “single ventricle” and “univentricular heart”, spark heated debate. In distant times, when congenitally malformed hearts were pathological curiosities, these entities were described as “cor triloculare biatriale”. Therein lies the beginning of the problem, since when hearts of this type were examined by more enlightened pathologists, such as the great Maude Abbott,1 it became plain that the apparently solitary ventricular mass in reality possessed a second, albeit much smaller, chamber. Abbott described this second structure as the “outlet chamber”. This convention of describing a “single ventricle”, albeit with a co-existing “outlet chamber”, that presumably lacked ventricular status, continued throughout the first half of the twentieth century, although it had been recognised by then that hearts could rarely be found with truly solitary ventricles, and these were typically deemed to be common structures. Van Praagh et al.2 neatly summarised the problem with this approach when they pointed out that the so-called “single ventricle” possessed two ventricular chambers, whilst the “common ventricle” described the truly solitary arrangement. In their seminal investigation of 1964, Van Praagh et al.2 analysed only those hearts unified because of double inlet atrioventricular connection, or alignment. They excluded arbitrarily from their investigation all hearts with atrioventricular valvar atresia, despite the similarity in morphology between many of these latter lesions and the hearts with double inlet.3