Cardiac gap junction channels are crucial for conduction of the electric impulse. Between cardiomyocytes there exist gap junctions constructed from connexin40 (Cx40), Cx43 and Cx45. A fourth isoform, Cx37, is expressed in the endothelial lining. Each of these channel types possesses specific properties and their functioning is regulated by various mechanisms. In this chapter we compare the physiological differences between these channels and discuss the factors involved in modulation of channel properties. Next, we evaluate how alterations in expression and differential regulation of channel properties affect cardiac impulse propagation.