en تخصصي Special پژوهشي Research <strong>Background</strong>: Hypothermia is usually used during cardiac surgery to further protect against cardiac and cerebral ischemia. However, cognitive impairment could be a common complication after open heart surgery. This study aims to determine the effect of rewarming on the cognitive status of patients after open heart surgery.&nbsp;<br> <strong>Methods</strong>: The present study was conducted as a double-blind, randomized clinical trial at Tehran Heart Center, Tehran, Iran. In this clinical trial, 80 patients referred for open heart surgery were selected and randomly assigned into the intervention (n=40) and control (n=40) groups. In the intervention group, rewarming the mattress was started after the patient entered the intensive care unit. Warming continued until the patient&rsquo;s body temperature reached the normothermia level (37&deg;C to 37.5&deg;C). The data were collected by demographic-clinical questionnaire and Mini-Mental State Examination at three time points: before, 7 days, and 1 month after the surgery. The data were analyzed in SPSS software, version 16 using descriptive statistics, independent t test, chi-square test, repeated measure ANOVA, and paired t test. The significance level was considered less than 0.05.<br> <strong>Results</strong>: The difference between the mean&plusmn;SD scores of cognitive status in the intervention group before the surgery (28.73&plusmn;0.87), 7 days (27.63&plusmn;1.03), and 1 month after the surgery (28.93&plusmn;1.21) was significant (P=0.008). The difference between the mean&plusmn;SD scores of cognitive status in the control group before the surgery (28.42&plusmn;1.02), 7 days (26.61&plusmn;0.86), and 1 month after the surgery (27.85&plusmn;1.06) was also significant (P=0.042). The results indicated that the mean score of cognitive status improves after 1 month, and it is greater in the intervention group (F=20.37, df=2, P<0.001). Significant differences were observed between the first and second time of measurements (P<0.0001) and also the second and third time of measurements (P<0.0001).<br> <strong>Conclusion</strong>: Rewarming patients after open heart surgery improves their cognitive status. Therefore, this procedure can be used as a safe and non-invasive method to prevent cognitive complications by nurses after open heart surgery. Rewarming, Hypothermia, Cognitive status, Postoperative complications, Thoracic surgery 25 34 http://jccnc.iums.ac.ir/browse.php?a_code=A-10-305-5&slc_lang=en&sid=1 Somayeh Haji-Jafari hajjafari.s1361@yahoo.com 10031947532846008820 10031947532846008820 No Trauma Nursing Research Center, Kashan University of Medical Sciences, Kashan, Iran. Seyed Hossein Ahmadi Tafti hosseinahmaditafti@yahoo.com 10031947532846008821 10031947532846008821 No Chief Surgeon & Director of Thoracic and Cardiac Surgery, Research Center for Advanced Technologies in Cardiovascular Medicine, Tehran Heart Center, Tehran University of Medical Sciences, Iran. Ismail Azizi-Fini azizifinies@yahoo.com 10031947532846008822 10031947532846008822 Yes Trauma Nursing Research Center, Kashan University of Medical Sciences, Kashan, Iran. Mahboubeh Rezaei m4.rezaei@gmail.com 10031947532846008823 10031947532846008823 No Trauma Nursing Research Center, Kashan University of Medical Sciences, Kashan, Iran. Fatemeh Atoof atoof@kaums.ac.ir 10031947532846008824 10031947532846008824 No Department of Biostatistics, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran.