Attempted cardioversion via the oesophagus (transoesophageal cardioversion) was compared with the transchest approach (transchest cardioversion) in a randomized trial of 100 consecutive patients with atrial fibrillation. For the transoesophageal group, 30, 50 and 100 J were delivered via an oesophageal electrode with subsequent 200 and 360 J transchest if required. For the transchest group, 50, 100, 200 and 360 J were delivered if required. In the transoesophageal group, 36/50 (72%) of patients cardioverted using the transoesophageal route alone, and in the transchest group, 41/50 (82%) of patients cardioverted (p = NS). First shock success was similar for the transoesophageal and transchest groups: 13/50 (26%) vs. 8/50 (16%) respectively. The mean number of shocks required to achieve successful cardioversion was identical for the transoesophageal and transchest groups (2.6). However, transoesophageal cardioversion was more successful than transchest cardioversion at energies < or = 100 J (36/50 [72%], and 17/50 [34%], p < 0.05). Median total energy for successful cardioversion was lower for patients in the transoesophageal group (180 J) than the transchest group (350 J) and mean peak current at successful cardioversion was also lower for patients in the transoesophageal group (21.7 A) than the transchest group (27.3 A) (p < 0.05). No oesophageal complications occurred. Thus, using an oesophageal electrode, cardioversion can be achieved as successfully as using the transchest route. The transoesophageal approach offers a low impedance, and consequently a low-energy pathway for cardioversion.