One of the differences between a mere accumulation of cells and a tissue or even an organ is that in organized forms (tissue, organ) cells typically communicate with each other. They coordinate their function, growth, and differentiation. In addition to cell adhesion molecules, increted hormones and local mediators, direct intercellular communication via gap junction channels plays a key role in this process. In cardiac tissue, these channels also provide the basis for the propagation of the action potential from cell to cell. Gap junction channels are dodecameric proteins consisting of connexin subunits of one (homomeric channels) or more isoforms (heteromeric channels). The connexins belong to an evolutionarily old protein family comprising 21 members in the mouse and 20 in man.1 In the mammalian heart typically three connexins are expressed: Cx43, encoded by the gene Gja1, is the most abundant; Cx40, encoded by Gja5, is confined to atria and the specific conduction system; Cx45, encoded by Gjc1, is found in early stages of development and in the specific conduction system, including sinus nodal cells. In recent years, murine Cx30.2, encoded by Gjd3, (the murine orthologue of human Cx31.9, encoded by Gjd3 Ref here?) and now Cx30, encoded by Gjb6, (see the report by Gros et al .2) have been found in the murine heart. Cx30 expression was limited to a narrow epicardial layer of the sinus node. Since Cx30-deficient … *Corresponding author. Tel: +49 341 865 1651, Fax: +49 341 865 1452, Email: dhes{at}medizin.uni-leipzig.de