Permanent tachycardia by reciprocal rhythm is an arrhythmia due to macro-reentry using the normal conduction pathways in anterograde direction and an accessory atrioventricular pathway, most often posteroseptal, in retrograde direction. It is sometimes worrying because of its chronicity and the deterioration in left ventricular function with which it may be associated. A case is reported of permanent tachycardia by reciprocating rhythm treated by radiofrequency. The diagnostic value, already shown by other authors, of stimulation of the upper part of the interventricular septum to confirm the participation of an accessory atrioventricular pathway in the tachycardia circuit is mentioned, and the need for extensive mapping, because of the recent description of non-postero-septal accessory pathways, is stressed.