Historical Background To the best of our knowledge, it was John Farre4 who first used the term transposition in the context of a cardiac malformation Subsequent to this description, it was usually considered that the aorta needed to be anterior to justify diagnosis, combined with support of the aortic valve by a muscular infundibulum However, some segmental combinations associated with an anterior aorta produce physiologic correction of the circulatory patterns, such that the systemic venous blood reaches the lungs despite being pumped by the morphologically inappropriate ventricle In two such combinations, there is also so-called anatomic correction, in that the aorta takes its origin from the morphologically left ventricle despite its anterior position In two additional variants, the circulations are in parallel rather than in series, despite the fact that the aorta arises in concordant fashion from the morphologically left ventricle It was this use of “corrected” in an anatomic sense, being dependent on the definition of transposition as an anterior aorta, that produced the potential for confusion.5 Further problems arose when it was recognized that the aorta could arise inappropriately from the morphologically right ventricle when in posterior position and with its valve in fibrous continuity with the mitral valve.6 It makes little sense, when considering clinical presentation, to describe a patient with an anterior aorta arising from the left ventricle as having “transposition” when the atrioventricular connections are also concordant, just as it makes little sense to suggest that patients with discordant ventriculoarterial connections, but with a posterior aorta, do not have transposition Thus, over recent years, there has been an increasing groundswell of opinion in favor of defining transposition on the basis of the origin of the great arterial trunks from morphologically inappropriate ventricles Therefore, the system that we currently use bases the use of “transposition” on the combination of specific atrioventricular and ventriculoarterial connections This is the solution now adopted by the International Working Group on Nomenclature and that which was advocated by the consensus statement prepared on behalf of the Society of Thoracic Surgeons.7 The approach recognizes the need also to describe, when appropriate, both arterial relationships and infundibular morphology In this way, all potentials for confusion are avoided Prevalence and Etiology Transposition was responsible for up to 20% of cardiac deaths in infancy prior to the era of surgical correction Although no definite etiologic factors have been identified, the condition is held to be more frequent in infants of diabetic mothers.8 Maternal intake of alcohol9 or poor nutrition10 during pregnancy may increase the risk of transposition in the offspring, whereas addition of folic acid to the maternal diet has been associated with reduced risk.11 Genetics Males are affected two to three times as frequently as females Transposition does not seem to coassociate with known major genetic disorders, and most cases are sporadic The increased presence of copy number variations in patients with transposition has allowed for identification of candidate genes.12 In general, genes affecting laterality and the nodal pathway have been associated with the disease.13,14