Study aim: Determining the Effect of Melatonin on Delirium After Cardiac Surgery Design: Two arm parallel groups randomized trial with blinded postoperative care and outcome assessment Settings and conduct: After obtaining permission from the Ethics Committee, the patients will be randomized to two groups of 30 (case and control). In the case of malathion, the control group will be given a placebo. Delirium incidence variables (based on CAM-ICU) and severity It (according to MDAS) is reviewed and recorded. Also, information on the duration of the operation, the duration of the cardiopulmonary bypass pump, the length of time required for mechanical ventilation after surgery, and the duration of admission to the ICU are recorded and compared in the two groups. Participants/Inclusion and exclusion criteria: inclusion criteria: 1-age 30 and above 2. Candidate for elective or semi-elective coronary artery bypass graft surgery (On-Pump CABG) 3. Risk of Anesthesia 1-3 4-Insensitivity to melatonin exclusion criteria: 1-No informed consent 2. Emergency surgery 3. Presence of melatonin inhibition, allergy to the drug or its compounds. 4. Chronic or recent use of melatonin or hypnotic drugs 5. Treated with barbiturates or anti psychotics 6. History of liver or kidney disease or chronic pulmonary disease Intervention groups: In the case group, a melatonin(Webber Naturals® Canada) dose of 3 mg, the night before the operation (8 nights) and the morning of the day (6 am) and night (8 nights) until 48 hours after the operation In the control group, the placebo (pharmaceutical gypsum) was prescribed the same day before the surgery (8 nights) and the morning of the day (6 am) and every night (8 nights) until 48 hours after the operation. Main outcome variables: Delirium incidence; Severity of Delirium; Mechanical ventilation time; Intensive care unit staying