Patients with mechanical heart valves have a high risk of thrombus formation on the valve and subsequent systemic embolism. These patients therefore need to receive life-long oral anticoagulation (OAC). Despite this treatment, the overall incidence rate of major thromboembolic complications is still about 1-2 per 100 patient-years. Additionally, these patients have an increased risk of bleeding complications, ranging between 1 and 7 per 100 patient-years. To reduce both types of often very serious complications, the optimal intensity of anticoagulation needs to be established. We found a fairly wide optimal range between 2.5 and 4.9 INR (international normalized ratio) at which the incidence of both untoward events was minimal. As a target intensity, we recommend opting for the middle of this range (INR 3.0-4.0), thereby providing a safe margin at both ends. In order to further reduce thromboembolic and bleeding complications, two approaches can be considered: first of all, the management of OAC treatment needs to be optimized in order to achieve a stable therapeutic effect in as many patients as possible. Secondly, patient characteristics need to be identified that increase the thromboembolic or bleeding risk. Subsequently, the optimal intensity may need to be adjusted accordingly, at an individual level. Possible risk factors for an increased thromboembolic risk are position and type of the prosthesis. Age may increase both the risk of thromboembolism and the risk of haemorrhage.