Environmental factors such as noise and light have been cited as important causes of sleep deprivation in Intensive care unit (ICU) patients. Previous studies demonstrated a hyperalgesic alteration in pain perception following a controlled sleep deprivation protocol. Another studies indicated that using eye masks can improve REM sleep in healthy subjects in simulated ICU environment, and improve sleep quality in ICU patients. This study aimed to determine the effects of using eye masks on sleep and thus on pain quality in postoperative cardiac surgery patients in ICU.