artery (Figure 2B), although the relationship to the artery varies from individual to individual. 8 The nodal cells are set in a matrix of fibrous tissue, with a relatively discrete boundary seen between the margins of the node and the adjacent atrial tissues (Figure 2B). 8 The earliest reconstructions of the node9 showed it to be a small discrete collection of tissues at the crest of the right atrial appendage, at the junction of the superior caval vein with the right atrium, but this is not typical. In a small proportion of cases, the node can extend across the crest of the right atrial appendage and occupy the interatrial groove. 10 More typically, however, the node is lateral and inferior to the crest. When reconstructed from serial sections, it is found to take the form of a cigar, with a tail of varying dimensions extending down the terminal crest toward the orifice of the inferior caval vein (Figure 2A). 8