This study compares effects of equipotent concentrations of halothane, enflurane, and isoflurane on atrioventricular (AV) function in dogs. Enflurane anesthesia was associated with more AV nodal depression, only at faster heart rates than either halothane or isoflurane. These rate-related effects are important in the genesis of supraventricular reentrant tachyarrhythmias. Subsidiary pacemaker function exhibited marked variability between and within animals with no demonstrable difference between anesthetic drugs. Enflurane has more depressant effects on AV nodal recovery properties than halothane or isoflurane; however, there were no differences demonstrated on slow AV nodal conduction. This suggests that enflurane would be the most effective volatile anesthetic in converting or slowing supraventricular tachyarrhythmias, while carrying no more risk of causing advanced heart block.