We previously demonstrated that α6 (Cx45), one of the three connexins of the mammalian myocardium, is preferentially expressed in the peripheral portion of the ventricular conduction system in rats and mice. Here we report that α6 is also prominently immunolocalized in the atrioventricular node and His bundle of these species. The distribution of immunolocalized α6 reveals that the node and bundle form part of an extended central conductive network circumscribing the AV and outflow junctional regions of the fetal, and less continuously, the adult heart. Of the three cardiac connexins, α6 is the isoform most continuously expressed by conduction tissues, and may thus account for the recently reported viability of the α5 (Cx40) knockout mouse. It is concluded that α6 expression is a defining feature of the heterogenous tissues comprising the atrioventricular conduction system of the rodent heart. Dev. Genet. 24:82–90, 1999. © 1999 Wiley‐Liss, Inc.