We tested the hypothesis that the effect of phasic vagal stimulation on atrioventricular (AV) conduction time is affected by the site of atrial pacing in anesthetized dogs. We paced the right atrium at a constant cycle length from the interatrial septum (IAS), superior coronary sinus (SCS), or inferior coronary sinus (ICS) regions, and we evaluated the time-dependent effects of vagal stimulation on AV conduction at each pacing site. When we stimulated the vagi at stimulus (St)-A phases greater than 136 +/- 40 ms and less than the phase that blocked AV conduction (182 +/- 70 ms), IAS pacing prolonged A-V intervals by 8.6 +/- 8.2 ms more than ICS pacing. A change in pacing site affected the A-V intervals by up to 30 ms when we stimulated the vagus at those times that caused the A-V intervals to prolong maximally. Furthermore, the effect of atrial pacing site on A-V intervals was modulated by AV nodal recovery times during the second or third cycles after the vagal stimulus.