OBJECTIVE: To investigate the relationship between arousal and nocturnal heart rate variability (HRV) in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS). METHODS: Twenty-seven patients with moderate to severe OSAHS who underwent overnight polysomnography (PSG) were enrolled, excluding patients with cardiopulmonary and nervous system diseases. An hour continuous PSG monitoring in non-rapid eye movement (NREM) was recorded for all patients. The mean heart rate (HR) in 10 s before each arousal and the peak HR in 10 s after arousal were compared, and the breathing disorder related arousal index (B-ArI) and pulse rate rise index (PRRI) were calculated at this time, and then a correlation analysis was performed. Furthermore, according to minimal oxygen saturation (minSaO(2)), 18 patients with moderate-to-severe OSAHS were matched into 10 events with and without EEG arousal in NREM, and then DeltaHR at apnea termination between these events were compared. RESULTS: The peak HR in 10 s after arousal onset [(81.6 +/- 9.4) beats/min] was significantly higher than the mean HR in 10 s before arousal onset [(69.6 +/- 7.3) beats/min, t = -14.87, P < 0.01], and B-ArI was positively correlated to PRRI (r = 0.97, P < 0.01). The DeltaHR of events with EEG arousal at apnea termination [(11.1 +/- 2.8) beats/min] was higher than those without EEG arousal [(7.0 +/- 2.4) beats/min, t = 4.702, P < 0.01]. CONCLUSIONS: The results indicate that arousal can influence the function of cardiovascular regulation. Frequent arousal is one of the main causes of the cardiovascular consequences in OSAHS patients.