BACKGROUND: An incidental lesion of the parasympathetic ganglia during circumferential pulmonary vein isolation (CPVI) may affect heart rate variability (HRV). AIMS: We studied the pattern of changes in HRV parameters and the relationship between the 1鈥憏ear HRV change following CPVI and the recurrence of atrial fibrillation (AF). METHODS: A total of 100 consecutive patients undergoing CPVI for paroxysmal AF were enrolled (mean [SD] age, 56 [11.2] years; 61 men). We measured HRV on the day before and after CPVI, and then at 1 month as well as 3, 6, and 12 months after CPVI using 24鈥慼our Holter monitoring. RESULTS: During the median follow鈥憉p of 33 months, 38 patients experienced the late recurrence of AF (LRAF). Compared with the pre鈥慍PVI values, HRV was significantly attenuated on day 1 after CPVI in all patients. However, at 3 to 6 months after CPVI, all HRV parameters remained significantly decreased in LRAF鈥慺ree patients but not in those with LRAF. The multivariate Cox analysis showed that early AF recurrence within the blanking period (hazard ratio [HR], 4.87; 95% CI, 2.44-9.69; P <0.001) and a change in the standard deviation of normal鈥憈o鈥憂ormal intervals (SDNN) observed 3 months after ablation (HR, 0.99; 95% CI, 0.98-1; P = 0.01) were associated with LRAF. The cumulative LRAF freedom after CPVI was greater in patients with an SDNN reduction of more than 25 ms reported 3 months after ablation than in those with a reduction of 25 ms or lower (log鈥憆ank P = 0.004). CONCLUSIONS: Sustained parasympathetic denervation during 12 months after CPVI was a marker of successful CPVI, whereas a 3鈥憁onth post鈥慍PVI SDNN reduction of 25 ms or lower predicted LRAF.