We reviewed twenty patients with mechanical prosthetic heart valves who underwent noncardiac operations which were performed in the presence of continual anticoagulant therapy. Prosthetic valves used were the SJM valve in nineteen patients and the Björk-Shiley valve in one. Twenty dental extractions in ten patients were performed with no reduction of warfarin, or the mean thrombotest value of 16%. Seven nonlaparotomy operations (polypectomy of the vocal cord in one patient, total hip joint replacement in one, insertion of a CAPD tube in one, pacemaker implantation in one, cataract operation in two and repair of tibial fracture in one) and three laparotomy operations (partial gastrectomy in two and hysterectomy in one) were performed under the thrombotest value of around 40% with partial reduction of warfarin. There was no difficulty in hemostasis during these operations. The only hemorrhagic complication in this series was bleeding from the abdominal wound in one patient two days after the gastrectomy when subcutaneous injections of heparin prolonged the ACT over 200sec. There were no thromboembolic complications. We conclude that dental extractions in patients with prosthetic heart valves can be safely performed with no reduction of warfarin and that the coagulability of thrombotest value of 40% is sufficient for hemostasis even in laparotomy operations.