The right atrioventricular junction and A-V node area in each of five human hearts was studied histologically in serial sections. The A-V node of a 54-year old female was reconstructed in four colors to provide a three-dimensional model of cardiac relationships, blood supply, and nodal configuration. The nodal fibers demonstrated two laminations. A superficial layer was composed of longitudinally oriented fibers, whereas a deeper layer was composed of oblique and transversely directed fibers. The atrioventricular bundle fibers were always continuous with nodal fibers of the deeper portion of the A-V node. Atrionodal fiber junctions occur along the superior, endocardial and inferior borders of the A-V node and impart to these surfaces a spiked appearance. The potential significance of A-V node structure to atrial cardiac conduction is presented.