The most important communication mechanism between cardiac cells is electrical transmission via low resistance pathways, the so-called gap junction channels. This book provides a comprehensive overview of what is known about cardiac gap junctions. An introduction into the various aspects of activation propagation and coupling in the heart is followed by a detailed description of the structure and diversity of gap junctions, including amino acid sequences and species variability. Subsequent chapters discuss their distribution, physiology and functions and the regulation of expression. The author then goes on to put these basic findings into a clinical context - the changes of gap junction distribution in the course of cardiac disease and their implications. A further chapter presents pharmacological approaches to the modulation of gap junction channel conductivity and outlines possible therapeutic strategies. The final part of the book describes the methods of investigation including double cell voltage clamp, immunohistochemistry, isolation procedures for gap junctions and dye coupling assays.