AbstractThis review summarizes the recent advances in understanding the development and function of the cardiac conduction system using genetically modified mice. Null mice for different cardiac connexins confirmed their suspected roles in cardiac conduction and, in addition, unraveled unexpected roles in cardiac morphogenesis. Genetically modified mice with LacZ‐labeled conduction system cells are indispensable tools to the further understanding of the mechanisms governing the development of this system in the mammalian heart. Mouse models also addressed the role and contribution of specific signaling molecules, such as PRKAG2, Nkx2.5, ALK3, and Tbx5, in the development of the cardiac conduction system and the pathogenesis of cardiac dysfunction in humans. © 2004 Wiley‐Liss, Inc.