A resurgence of interest in atrial fibrillation has led to research in several avenues. Observations on the behavior of the atrium during atrial fibrillation demonstrate that electrical activity is not entirely random and that sinus node activity persists despite surrounding fibrillation. Anticoagulation therapy for chronic atrial fibrillation is now accepted as optimal treatment, but randomized trials have excluded the majority of patients screened and the risk-benefit ratio of therapy in the average patient therefore remains unclear. This is being addressed in comparative trials of warfarin and aspirin and in an analysis of risk factors for stroke derived from a major trial. Assessment of the efficacy of therapy for the control of ventricular rate in atrial fibrillation has underscored the slow action of digoxin and raised the issue of suboptimal dosing. With the recognition that improvement of exercise capacity following cardioversion may be postponed for weeks, several studies have evaluated serial changes in ventricular function and shown that in some patients sinus rhythm is associated with an improved ejection fraction. Transesophageal echocardiography is an area of intense interest for the identification of patients at high risk of thromboembolism following cardioversion, and the significance of left atrial spontaneous echo contrast as well as the left atrial appendage contractile function are being investigated. Finally, new methods of arrhythmia termination are being evaluated and developed, and surgical approaches to atrial fibrillation are being expanded and refined.