Objectives: Epicardial fat pads contain cardiac ganglionated plexi of the autonomic nervous system. Autonomic denervation may improve the success rate of atrial fibrillation (AF) ablation. This study was designed to elucidate the effects of right atrium-pulmonary vein (RA-PV) and left atrium-inferior vena cava (LA-IVC) fat pads block using botulinum toxin injection on the electrophysiological characteristics and AF inducibility. Methods & Results: Eight mongrel dogs were studied with following protocol. Both cervical vagal stimulation (VS) was applied (20Hz, 0.2ms, 5.6짹2.0 V) to decrease the sinus rate by approximately 50% from baseline. In addition, AV nodal function was evaluated by measuring ventricular rate (VR) during rapid atrial pacing (RAP) with cycle length of 50 ms. Finally, AF inducibility was evaluated with burst pacing with 200 impulses at 50-ms cycle length. Through median thoracotomy RA-PV and LA-IVC fat pads were exposed. Boltulinum toxin was injected to the whole areas of both fat pads (50 U at each fat pad). VS was then applied to determine effects on sinus rate, AV node, and AF inducibility. The same protocol was repeated at 1-5 hours later. The results are illustrated in the Figure. Conclusion: VS effects on the sinus node, AV node, and AF inducibility were significantly eliminated at 4, 2, and 3 hours after botulinum toxin injection, respectively. These changes were not observed in saline-injection animals. Therefore, short-term suppression of AF induction could be achievable by botulinum toxin in this canine model.