The newest tupes of mechanical prosthetic valves have been shown to be long-lasting and haemodynamically irreproachable. However, they are inadequate with respect to thromboresistance. Modern oral anticoagulant therapy is far from ideal. Every patient, with more or less thrombogenic mechanical valve, carries a risk not just for valve thrombosis or sistemic emboli, but also a risk of bleeding which follows anticoagulant therapy. Thromboemboli and haemorrhage comprise 75% of complications occurring in patients with mechanical heart valves (Edmunds 1987). The decreased incidence of thromboembolic complications registered in the last several years is most likely due to more careful and consistent anticoagulant therapy, revision of indications for the surgical act and improved thromboresistance of the new valve prostheses. The adjunctive value of antiplatelet drug is still a matter of controversy, despite reports of positive results due to these agents. It appears that the combination of pelentan and persantin is optimal, whereas aspirin is not recommended because of frequent gastrointestinal bleeding. Aspirin alone fails to provide adequate protection for valve prostheses in adults even when they are bileaflet in the aortic position. In pregnant women, adolescents and during subsequent surgical treatment, oral anticoagulant therapy should be modified appropriately.