Introduction: Atrial fibrillation (AF) is the most common arrhythmia to occur aftercardiac surgery. An exaggerated systemic inflammatory response has been proposedto be one etiological factor.· Aim of the study: This study was done to test whether perioperative intravenouscorticosteroid administration -as a potent antiinflammatory- after cardiac surgeryprevents AF.· Patients and methods: The study involved 100 consecutive patients without priorAF who had done their first on-pump coronary artery bypass graft (CABG) surgery,aortic valve replacement (AVR), or combined CABG and AVR surgery from April2009 to January 2010 in Cairo university hospitals and National Heart Institute.Patients were divided into two groups, group 1 (50 patients) who received 100-mghydrocortisone in the evening of the operative day, then every 8 hours during thenext 3 days and group 2 (50 patients) who did not given hydrocortisone. All patientsreceived oral bisoprolol in dose titrated to heart rate. Main outcome measure was theoccurrence of AF during the first 72 hours after cardiac surgery.· Results: The incidence of postoperative AF was significantly lower in thehydrocortisone group (14/50 [28%]) than in the other group (24/50 [48%], despiteincidence of DM was statistically significant higher in the hydrocortisone group(30/50 vs 20/50 patients, P=0.046). The hydrocortisone Group patients had 0.583(95% CI 0.184 - 0.966) probabilities compared to other group patients to developAF in the 1st three postoperative days; P=0.039). TLC was significantly lower in thehydrocortisone group than the other group during the first three postoperative days(P<0.05). Patients received hydrocortisone did not have higher rates of superficial ordeep wound infections, or other major complications.· Conclusion: Intravenous hydrocortisone was effective and safe in reducing theincidence of AF after cardiac surgery.