Those who treat patients diagnosed with so-called hypoplastic left heart syndrome are well aware that the syndrome is made up of several phenotypic entities.1 This important fact, however, is not always appreciated by those seeking to establish the genetic cues predisposing toward development of the lesion.2 If we are to establish the reasons that some infants are born with the syndrome, it will be optimal if we can agree on the phenotypic variables to be included. In this regard, at least in the clinical setting, there is now agreement that one of the required features is the integrity of the ventricular septum, and the presence of concordant ventriculoarterial connections.
