Objectives: Autonomic denervation can suppress atrial fibrillation (AF) vulnerability. This study was designed to elucidate the long-term effects of ganglionated plexi block using botulinum toxin injection on the electrophysiological characteristics and AF inducibility. Methods & Results: Six mongrel dogs were studied. Through right lateral thoracotomy two major epicardial fat pads (RA-PV and LA-IVC fat pads) were exposed. Botulinum toxin (BT, 50 U at each fat pad, n=4) or normal saline (NS, n=2) was injected to the whole areas of two fat pads. After 2 weeks (two dogs in BT, one in NS) and 4 weeks (two in BT, one in NS), following study protocol was applied. Sinus rate, ventricular rate during rapid atrial pacing with cycle length of 50 ms, and AF inducibility were measured with and without vagal stimulation (VS). Both cervical VS was applied (20 Hz, 0.2 ms, 5.0 V). AF inducibility was evaluated with burst pacing with 200 impulses at 50-ms cycle length. VS effects on the sinus node and AV node were observed during the follow-up. AF inducibility during VS was 0% vs. 75% (BT versus control) in 2 weeks, but 100% vs. 100% in 4 weeks. Conclusion: VS effects on the sinus node and AV node were intact after botulinum toxin injection during long-term follow-up. However AF was not inducible in BT through 2 weeks. AF inducibility was restored in 4 weeks. Therefore, temporary suppression of AF induction at least for 2 weeks could be achievable by botulinum toxin injection in this canine model.