Current heart valve prostheses may be classified as either mechanical or tissue valves (bioprostheses). The principal advantage of mechanical devices is their established long-term durability; however, chronic anticoagulation is recommended to reduce the incidence of thromboembolic complications. Tissue valves are associated with a relatively low rate of thromboembolism but their durability level has not been determined. All contemporary prosthetic heart valves yield comparable survival rates.