The advent of radiofrequency catheter ablation to terminate A-V nodal reentrant tachycardia (AVNRT) has been a revolutionary advance in the clinical treatment of one of many types of cardiac arrhythmias. From a basic science standpoint, prevailing views regarding antegrade (A-V) and retrograde (V-A) conduction have been found to be seriously deficient and there is, therefore, a need for new concepts to be developed based on a better understanding of the structure and physiology of the A-V junction.