The vagal system regulates the atrioventricular conduction time (T_AV) via two opposing mechanisms: a direct effect on the atrioventricular node and an indirect effect through changes in heart period (T_AA). To evaluate how dynamic vagal activation affects T_AV, we stimulated the vagal nerve with frequency-modulated Gaussian white noise and estimated the transfer function from vagal stimulation to the T_AV response under conditions of no pacing and constant pacing in anesthetized cats. The effect of changes in T_AA on T_AV was estimated by a random-pacing protocol. The transfer function from vagal stimulation to T_AV has low-pass filter characteristics. Constant pacing increased the maximum step response in T_AV (2.4 ± 1.2 vs. 6.3 ± 2.2 ms/Hz, P < 0.01). The time constant did not differ between the vagal effect on T_AV and that on T_AA (2.9 ± 1.2 vs. 2.3 ± 0.5 s). Because changes in T_AA reciprocally affected T_AV without significant delay, the direct and indirect effects were dynamically counterbalanced and exerted stable T_AV transient response during vagal stimulation under normal sinus rhythm.