Paroxysmal AF associated with focal ectopy originating from the pulmonary veins (PVs) can be preceded by variations in autonomic tone, however the underlying cellular mechanisms are not clear. To determine the mechanisms of autonomically mediated PV ectopy, high resolution optical mapping techniques were used to measure action potentials and calcium transients from the pulmonary vein and ligament of marshall area in the arterially perfused canine left atrium. Rapid pacing was used to initiate ectopic activity during pituitary adenylate cyclase-activating polypeptide (PACAP) injection (1 nmol), as a surrogate for autonomic imbalance, before (n=9) and after (n=6) verapamil (10 nmol). In all preparations, spontaneous activity was absent before rapid pacing. During PACAP, rapid pacing induced ectopic activity in 8 of 9 preparations. In contrast, before PACAP rapid pacing did not induce ectopic activity. Activation maps of each episode of ectopic activity indicated that the site of origin occurred more frequently in the pulmonary vein area (70%) compared to the ligament of marshall area (30%). As rapid pacing cycle length increased, so did the ectopic beat coupling interval. In addition, PACAP-induced ectopic activity was associated with large calcium transient amplitudes and was always suppressed by verapamil, a Ca²⁺ channel blocker (p<0.05). Finally, during PACAP in the absence of an ectopic beat, spontaneous calcium release and delayed after depolarizations were observed simultaneously after termination of rapid pacing . In conclusion, these data suggest that autonomically mediated PV ectopy may be due to calcium-mediated triggered activity arising from delayed after depolarizations.