Direct-current cardioversion is a common treatment modality for acute termination of atrial flutter in neonates. Studies in children have demonstrated that cardioversion is often successful with as little as 0.25-0.5 J/kg with the current biphasic devices. We hypothesize that during cardioversion of atrial flutter in neonates, however, the impedance may be high and more energy may be required for successful cardioversion. A retrospective chart review of our institutional experience from 2005 through 2008 was performed. Neonates with atrial flutter requiring cardioversion who had strips available for review were included. Six patients met the inclusion criteria. The median age at the time of cardioversion was 2.6 h (range, 1.3-336 h) and the mean weight was 3.22 +/- 0.4 kg (SD). The mean electrical impedance of the successful shocks was elevated, at 234 +/- 136 Omega. The mean energy delivered for successful cardioversion was 0.9 +/- 0.3 J/kg, and the current was 1 A in all patients. In conclusion, the shock impedance was elevated in the neonates studied during cardioversion of atrial flutter. Low current was sufficient for successful cardioversion. Further studies are needed in this specific population.