OBJECTIVE: Myotonic dystrophy type 1 (DM1) is a hereditary myopathy characterized by an autosomal dominant inheritance with important cardiovascular and autonomic deregulation. DM1 patients have a high prevalence of obstructive sleep apnea (OSA), but the effects of this comorbidity on cardiovascular autonomic control (CAC) are unknown. The present study aimed to investigate CAC during sleep-wake cycle in DM1 patients, taking into account the effects of OSA comorbidity. METHOD: Twenty-three patients with a diagnosis of DM1, and a control group, underwent a complete polysomnographic study (PSG). Electrocardiogram and respiration were extracted from PSG, divided according to the sleep stages, and analyzed using spectral analysis (SpA) of heart rate variability (HRV). SpA identified three components: very low frequency (VLF), low frequency (LF), a marker of sympathetic modulation, and high frequency (HF), a marker of vagal modulation. RESULTS: The results showed that in DM1 patients, the sympathovagal balance shifted towards a vagal predominance during non-rapid eye movement (NREM) sleep and a sympathetic predominance during rapid eye movement (REM) sleep. Second, this preserved cardiac autonomic modulation was not affected by the comorbidity with obstructive sleep apnea syndrome (OSAS). Third, in DM1 patients, OSAS comorbidity was associated with a reduction in HRV during the whole sleep-wake cycle. Lastly, in DM1 patients with OSA, cardiorespiratory coupling was reduced compared to controls. CONCLUSIONS: DM1 patients had preserved cardiac autonomic dynamics during NREM and REM sleep, and this phenomenon was not affected by the presence of OSA. However, the comorbidity with OSA was characterized by a reduction in total HRV, which is a marker of the ability of autonomic control to respond to stressors stimuli.