ABSTRACT
Sinus Node The sinus node is a tapered cylindrical structure that lies subepicardially at the junction between the right atrium and the superior vena cava. Histologically, the sinus node consists of several cell types that are embedded within a connective tissue stroma. Round or ovoid P cells are probably the site of impulse formation, and transitional cells, which are considerably greater in number, serve as the link between the P cells and the remaining atrial tissue (Fig. 1).
