We retrospectively assessed our experience with the use of bipolar atrial epicardial electrodes in 70 consecutive patients following open-heart surgery. These patients, representing 1 month's experience on one of our cardiac surgical services, are a random sample of our total experience with more than 6.000 patients in whom we have routinely placed such electrodes. The atrial wire electrodes were used diagnostically and/or therapeutically in 57 patients a total of 139 times. In only 13 patients were the atrial wires not used for any reason. Atrial electrograms were recorded 63 times in 34 patients, 41 times to establish a diagnosis of an arrhythmia and 22 times to confirm the diagnosis of an arrhythmia originally suspected from interpretation of a standard or monitor electrocardiogram (ECG). Atrial pacing was used to treat abnormalities of rhythm or conduction or both in 75 instances in 49 of the 70 patients. Because of their great utility in the diagnosis and treatment of arrhythmias, we conclude that routine placement of atrial wire electrodes at the time of operation is indicated regardless of the nature of the open-heart procedure or the preoperative rhythm.