The aim of this study was to investigate the effect of sevoflurane and desflurane on cardiac arrhythmias in adult patients who will be anesthetized. A total of 40 patients who were in the ASA I–II group and who were to undergo elective surgery were included in the study. No pre-medication was administered to the patients. They were monitored with the Holter equipment at preoperative 24 hours, and also at postoperative 24 hours on condition that Holter monitoring will begin before induction. Following routine monitoring, the patients were randomly divided into two equal groups; group one was given sevoflurane and group two was given desflurane. In this study, desflurane and sevoflurane resulted in both a significant prolongation of QT and QTc and a significant increase in QT and QTc dispersion when compared with the basal values. In the sevoflurane group, there was no significant increase in postoperative ventricular arrhythmia, compared to that during the preoperative period. However, this increase was significant in the desflurane group (p = 0.009). Sevoflurane and desflurane result in an increase in QT dispersion. Postoperative rhythmic control should carefully be monitored, especially in the desflurane group.