A [human] case of the permanent form of junctional reciprocating tachycardia was studied by endocardial and epicardial mapping. The retrograde impulse penetrated the atrium in 2 different areas: one near the region of the recorded His potential and the other near the orifice of the coronary sinus. Retrograde conduction persisted after the surgical creation of complete antegrade heart block, suggesting the existence of an accessory ventriculo-atrial connection. The decreased retrograde conduction observed suggests that an accessory ventriculo-atrial node may be the underlying structure for activation of this arrhythmia.