Atrial fibrillation (AF) and atrial flutter (AFL) are arrhythmias that commonly occur following cardiac surgery. The precipitating events are not always obvious, although predisposing factors including age have been defined. Postoperative AF and AFL add significantly to both the cost and morbidity of cardiac surgery. This guideline report, which was created under the auspices of the American College of Chest Physicians (ACCP), critically reviews evidence-based literature defining optimal treatment and prophylaxis for postoperative AF. Specific issues addressed include the following: (1) controlling the ventricular response rate in the patient with postoperative AF and AFL; (2) preventing thromboembolism in the setting of AF and AFL including the appropriate role of anticoagulation therapy; (3) pharmacologic approaches to converting AF or AFL to normal sinus rhythm, and maintaining normal sinus rhythm postoperatively; and (4) pharmacologic and surgical prophylaxis against postoperative AF and AFL. The resulting clinical practice guidelines represent the best-supported treatments, based on a rational scientific approach formulated from randomized clinical trials and systematic reviews. The panel convened by the Health and Sciences Policy Committee of the ACCP reviewed the currently available evidence to provide a basis for making specific recommendations for patient care.