Sleep-related painful erections (SRPE) are characterized by penile pain that occurs during erections, typically during REM sleep. Afflicted individuals usually have normal erections during wakefulness. The disorder could be related to an altered autonomic function only during sleep. The aim of this study was to evaluate tonic and phasic heart rate (HR) modifications during sleep in 10 SRPE patients compared to 25 age-matched controls. A reduced cardiac vagal activity during sleep, as well as a trend towards a higher HR acceleration in relation to spontaneous body movements, have been found in SRPE patients. The possible beta-adrenergic hyperactivity during sleep in these patients could explain the reported efficacy of a beta-blocker, such as propranolol, in this disorder.