Purpose: clinical trial comparing the impact of Selenium, Vitamine C And N-Acetylcystein (NAC) on prevention of acute kidney injury following off-pump CABG. This study is perspective, randomize and not blinded. 320 Patients had been studied by random number table in one of 4 groups (each group 80 patients) selenium, vitamin C, NAC and blank group. In first group 500 mg oral selenium (the trade name Selenase made by Biosyn Pharmacy company) was used in 14 hours before surgery, the dose was repeated 2 hours before surgery again. In vitamin C group, 1500 mg of Vitamin C (made by Exir, Tehran drug and Osve pharmacy companys) as 3 effervescent tablets, that 14 hours before surgery, the dose was repeated 2 hours before surgery again. NAC group received 600 ml/gr NAC (made by Exir pharmacy company) effervescent tablets 14 hours before surgery, the dose was repeated 2 hours before surgery again. Patients in the control group received only the routine care standard. In all of the patients, drug administration, as every 12 hours orally or by nasogastric gavage continued until 3 days after surgery, after surgery patients received a total of 8 doses of drugs.The total daily prescribed drugs to patients was 1,000 mcg of selenium, 3 grams in vitamin C group and NAC groups was equal to 1200 mg. Inclusion criteria: patient satisfaction; off-pump coronary artery bypass graft surgery method; there is no known history of renal including structural abnormalities; kidney failure or patients with a single kidney; non-emergency coronary artery bypass graft. Exclusion criteria: patients with chronic obstructive pulmonary disease; usage more than 2 units of blood during surgery; history of taking non-steroidal anti-inflammatory drugs; acute sepsis; patients with severe malnutrition; diabetes. Primary outcome: acute kidney injury in the form of increased serum creatinine or decreased urine output or both will be determined. Secondary outcome: stay in ICU