A 63 year old man with ischemic heart disease underwent two sessions of catheter ablation in the inferior right atrium for poorly tolerated resistant and recurrent atrial flutter. After endocavitary mapping and comparison with surface recordings of the f waves, a shock of 50 joules was delivered to the zone situated anteriorly to the inferior vena cava, under the orifice of the coronary sinus and behind the tricuspid valve. Early recurrence of the arrhythmia led to a second attempt and another 50 joules shock was administered to the same area. Another short term recurrence led to definitive nodohisian interruption with a 270 joules shock. Thirty months later, the patient died suddenly during an episode of cardiac failure. Macroscopic examination of the right atrium showed a zone of parietal congestion measuring 4 x 3 cm with a very thin, translucid, central zone measuring 3 x 1.5 cm, just anterior to the inferior vena cava in the right atrial free wall. Histological examination of this zone showed an intense, mutilating fibrosis dissociating the muscular fibres, of the pectinate muscle and even replacing the myocardium in certain regions. In the Eustachian valve, there were muscular fibres, probably representing the posterior internodal pathway, which were also fibrosed. These observations suggest that: 1) in view of the extreme thinness of the atrial wall at the site of ablation there is a high risk of perforation even when right endoatrial catheter ablation is performed with low energy shocks; 2) the posterior internodal pathway does not seem to be an essential component for atrial flutter.