Changes in sympathetic and vagal tone may be the substrate for the development of cardiac arrhythmias in patients with obstructive sleep apnea (OSA). The cardiovascular responses in the traditional autonomic tests show great interindividual and intraindividual variations. During sleep there are repetitive modifications of heart rate (HR) that are not influenced by psychologic factors or the patient's cooperation. For this reason, we evaluated HR modifications in relation to spontaneous body movements (BM) and sleep apneas during nonrapid eye movement (NREM) and rapid eye movement (REM) sleep in habitual snorers with normal and pathologic respiratory disturbance index (RDI). From 132 consecutive patients referred to our sleep center for habitual snoring and/or daytime somnolence, we selected 35 male patients younger than 60 years without clinical evidence of autonomic dysfunction. They were divided into three groups: group A (RDI < 10); group B (RDI > 10 and < 20); and group C (RDI > 20). No significant difference was found among the three groups in the HR variability related to BM. In the evaluation of bradytachyarrhythmias related to apneic events of 20 to 30 s, we found a significant difference between group A and the other two groups. In patients with RDI > 10, a reduced HR variability related to a reduced sympathetic tone in the post-apnea phase was observed. Some authors suggested that an HR increase during the post-apnea period can be used as an index of "brainstem arousal." Our results seem to indicate a reduced apnea-related "arousability" in patients with RDI > 10. This finding might be one of the factors contributing to the worsening of OSA.