The authors report their experience involving 21 right endoatrial electroversions aimed at converting chronic atrial fibrillation resistant to external electroversion. All prior precautions were taken to ensure that the shocks were not in contact with an atrial wall nor over the node-His bundle (two dimensional radiological identification, endocavitary recordings). A total of 37 internal electric shocks were administered. Results were: 16 immediate successes out of 21 (72.2 per cent) and 12 short term successes out of 21 (57 per cent). The mean effective energy value was 200 Joules. There were no traumatic complications. The authors conclude that this technique is effective and reliable in the management of atrial fibrillation resistant to external electroversion.