Clinicians are often required to decide how to manage patients receiving long-term anticoagulant therapy, and who need a surgical procedure. The decisions are based on the perceived risk of continuing or stopping the treatment. Generally, warfarin must be stopped before all interventions at high risk of bleeding, but can be maintained unchanged before oral and skin surgery. For patients with a high risk of thromboembolism, heparin should be administered preoperatively, when the INR is <2. The estimation of this risk depends largely on the undelying heart disease. In the postoperative phase, the restarting of anticoagulant therapy must be weighed against both thromboembolic and hemorragic risks.