AIMS: Sleep apnea (SA) is a risk factor for atrial fibrillation (AF) occurrence. Sympathovagal imbalance is a mechanism that predisposes to the development of AF and that occurs in SA. Some pacemakers can detect SA events and continuously measure a time domain measure of heart rate variability (HRV), i.e. the standard deviation of 5-min median atrial-atrial sensed intervals (SDANN). We evaluated the association between the occurrence of AF and device-detected SA and SDANN in patients who received pacemakers. METHODS: We enrolled 150 consecutive patients undergoing implantation of a dual-chamber pacemaker, capable of SA and SDANN estimation. The SA was defined as severe if the Respiratory Disturbance Index was >/=30鈥痚pisodes/h for at least one night during the first week after implantation. RESULTS: Sixteen patients in permanent AF were excluded from our analysis. During follow-up, AF (cumulative device-detected AF duration鈥?鈥?鈥痟/day) occurred in 24(18%) patients out of the remaining 134 patients. Severe SA was detected in 84 patients. SDANN values were available in 74 patients and the median value was 76鈥痬s [25 degrees -75 degrees percentile:58-77]. The risk of AF was higher in patients with severe SA (log-rank test; p鈥?鈥?033). The presence of either or both conditions (severe SA and SDANN鈥?鈥?6鈥痬s) was associated with shorter time to AF event (p鈥?鈥?042) and was an independent predictor of AF (hazard ratio: 2.37; 95%CI:1.08 to 5.21; p鈥?鈥?033). CONCLUSION: In pacemaker patients, device-diagnosed severe SA and reduced SDANN are associated with a higher risk of AF.