Objectives: Action potential duration restitution (APDR) is governed by multiple ion-channel kinetics, and the function of these ion channels is modulated by the autonomic nervous system. Therefore, vagal activation may affect APDR, but this hypothesis has not been evaluated. This study was designed to demonstrate the effects of vagal stimulation on the atrial electrical restitution property. Methods & Results: Seven mongrel dogs were studied. Vagal stimulation (VS) was applied at the right cervical vagus nerve at intensities to decrease the sinus rate by approximately 50%. Typical parameters for the cervical VS trains were frequencies of 20 Hz at pulse amplitude of 1.2짹1.1 mA (0.5 – 3.5) and a pulse width of 0.2 ms. Electrocardiographic and atrial electrograms were recorded during programmed pacing and monophasic action potential recordings were performed on the epicardial surface of the appendages (RAA, LAA) and free walls (RAFW, LAFW) of both atria. The APDR curves were constructed by plotting the APD90 versus the preceding diastolic interval (DI). The major results are illustrated in the Figure. VS increased the steepness of the maximum slope (left), flattened the slope at DI > 100 ms (middle), and significantly increased the spatial dispersion of APDR curve in atrial compartments (right). Conclusion: The reported effects might be one of the arrhythmogenic mechanisms of VS in the atrium. Changes in APDR could provide rationale for vagal denervation in AF treatment.