Potentials recorded at various sites in the atrioventricular (A-V) conduction system indicate that conduction is continuously electrical in nature and involves no synapse-like (i.e., chemical) conduction. The region between atrium and atrioventricular node has the slowest conduction velocity (.05 M./sec.) and lowest safety factor. Conduction through the A-V node is at about .12 M./sec. Results demonstrate shapes of potentials recorded extracellularly at various sites within the A-V node, first degree and complete block during rapid atrial stimulation, and echo-like phenomena.