Recently ablation surgery for atrial fibrillation, so-called maze procedure, has become popular. However, this procedure usually needs cardiopulmonary bypass. Here we describe 3 patients for whom the simple, new procedure in which epicardial radiofrequency ablation is sucessfully done without cardiopulmonary bypass prior to concomitant cardiac operation. Our modified maze procedure consists of isolation of pulmonary veins using the FLEX 7 radiofrequency ablation device (COBRA). Following the surgery, all patients quickly attained regular sinus rhythm. We believe our procedure would be especially useful for patients for whom concomitant cardiac procedure can be done on beating heart.