Although various degrees of sleep-cycle alterations are reported after ischemic events, their clinical importance is usually neglected in context of the other more severe neurological abnormalities. The aim of this study was to experimentally test whether alterations of sleep-cycles occur even after a minimal ischemic cerebral injury. Specifically, we investigated the changes in slow-wave-sleep (SWS) patterns following a 5-minute transient global cerebral ischemia (GCI) in the rat, which is known to cause only a small ischemic injury of the hippocampus. Experiments were carried out in freely moving adult male Wistar rats, accommodated to a 12h dark/light cycle. A telemetric device was implanted for wireless EEG and neck EMG recordings. After 2 days of baseline telemetric recordings, GCI was induced using a variation of the "4-vessel occlusion" model under chloral-hydrate anesthesia, and recordings were continued for at least 2 more days.. To avoid the effects of anesthesia recovery, the first 12 hours recordings following GCI were excluded from the analysis. The SWS epochs were identified as continuous segments with high-amplitude delta EGG activity, low neck EMG activity and low movement activity at video tracking, using a custom-software with operator-adjustable thresholds. In rats, the sleep is fragmented in many SWS epochs covering about 40% of 24-hours. Nevertheless, rats being nocturnal animals, the total SWS was about 30% longer during the 12-hour light cycles than during the 12-hour dark cycles. Following GCI, there was an increase in total SWS time which attenuated its variability between the light and dark cycle period. Our preliminary data indicate that even a minimal cerebral ischemic injury leads to sleep-cycle alterations in rat. This raises hope that prognostic markers of ischemic injury can be derived from quantifying early sleep patterns.