The risk of thrombo-embolic episodes in patients with artificial heart-valves has been reduced by means of improved material and of anticoagulation. Kinetic studies, however, indicate a correlation between the risk of thrombo-embolism and an increased platelet turnover. Therefore a therapy with platelet aggregation inhibitors has been recommended. In addition to an increased platelet turnover, other risk factors have been evaluated like the material, the number, and the position of the artificial valves, the time elapsed since surgery, cardiologic disease, and anamnestic criteria. We proposed a semiquantitative risk score taking in account all these risk factors to avoid unnecessary coagulation treatment and to recommend antiplatelet therapy, where necessary. This risk score could be a basis to evaluate controlled studies.