BACKGROUND: Sympathetic hyperactivity and poor sleep quality are reported in myocardial infarction (MI) patients and angiotensin-converting enzyme inhibitors (ACEI) can improve long-term survival in these patients. We aimed to evaluate ACEI effects on cardiac autonomic activity (CAA) and disordered sleep patterns in ambulatory rats after MI. METHODS: Polysomnographic recording was performed in sham (n = 8) and MI (n = 9) male rats during normal daytime sleep before and after captopril treatment. Spectral analyses of the electroencephalogram and electromyogram were evaluated to define active waking (AW), quiet sleep (QS), and paradoxical sleep (PS). Central sleep apnea (CSA) events were measured by analyzing the electromyogram of the diaphragm. CAA was measured by power spectrum analyses of heart rate variability (HRV). RESULTS: In the MI group, there was a higher low frequency/high frequency ratio during sleep, which reduced significantly after captopril treatment, especially at the QS stage compared to that before captopril treatment. The frequency of sleep interruption was higher in the MI group than the sham group. Increased AW and PS, and decreased QS times were noted in the MI group compared to the sham group. These changes were restored to baseline after captopril treatment in the MI group. CSA events were significantly increased in the MI group, and were restored to the normal level after captopril treatment. CONCLUSIONS: Our results demonstrate significant sleep fragmentation with sympathetic hyperactivity after MI, and that captopril restores the autonomic dysfunction and sleep disorder. These findings suggest that ACEI improved sleep-related respiration disorder after MI by restoring autonomic homeostasis, and provide a hypothesis generating for future studies in humans.