OBJECTIVE: Patients with non-organic erectile dysfunction (ED) frequently present with syndromes involving systemic sympathovagal dysfunction. The linkage of ED to cardiac autonomic regulation is not well understood. METHODS: Forty-four men with non-organic ED and 38 healthy age-matched control subjects with ages ranging from 40 years to 69 years were recruited. These two groups were divided into three distinct age categories at 10-year intervals. Patients were divided into three different severity categories, among whom 35 patients received a two-month oral treatment of trazodone. Power spectral analysis of successive R-R intervals (RR) was performed to evaluate the variance (variance of RR-interval values), the high-frequency power (HF), and the ratio of low-frequency power to HF (LF/HF) of their heart rate variability (HRV). RESULTS: Patients exhibited a significantly lower variance and HF, but a higher LF/HF compared to the control group across all age categories. The changes in variance and HF were severity dependent. In addition, all the HRV parameters of the patients with a satisfactory response after treatment have significantly improved. CONCLUSION: The results indicate that patients with non-organic ED had significant cardiac sympathetic hyperactivity and severity-dependent cardiac vagal impairment. SIGNIFICANCE: Non-organic ED may be accompanied by an abnormality in cardiac autonomic regulation.