This paper presents successful surgical treatment of a-trial fibrillation by a simplified maze procedure (SMP) in 3 patients. All of them suffered from rheumatic heart valvular diseases complicated with atrial fibrillation (AF) for 3 to 10 years. Their heart function were in class III-IV(NYHA). The diameter of the left atrium varied from 52-58 mm and the cardiothoracic ratio 0. 64-0.70. The open heart operation was performed under conventional cardiopulmonary bypass combined with systemic hypothermia and using cardio-plegia for myocardial protection. After finishing the modified maze operation,mitral valve replacement was performed in 2 cases and mitral and aortic valve replacement together with tricuspid annuloplasty in one. Sinus rhythm recovered after cardiac ressuscitation and was maintained in the early postoperative period in all 3 cases. However, with in 3 months after the operation, one patient died of cerebrovascular accident, probably a complication of anticoagulant therapy. The other 2 patients remained well with normal sinus rhythm and their heart function was in class I 3 years after the operation. The clinical results indicate that mitral valve or mitral and aortic valve replacements plus simplified maze procedure to abolish atrial fibrillation may improve the postoperative hemodynamics by recovery of the sinus rhythm.