Newer surgical bioprosthetic valves may show greater freedom from struc- tural deterioration, specifically in the older indi- vidual, although a high late mortality rate in these studies may preclude recognition of valve dys- The risks of bleeding and throm- boembolism with mechanical prostheses are low, especially in compliant patients with appropriate INR monitoring. Several studies have shown a sur- vival advantage with a mechanical prosthesis in this age group. Alternatively, large retrospective observational studies have shown similar long- term survival rates in patients 50 to 69 years of age undergoing mechanical versus bioprosthetic In general, patients with mechanical valves experience a higher risk of bleeding because of anticoagulation, whereas individuals who receive bioprosthetic valves expe- rience a higher rate of reoperation attributable to structural deterioration of the prosthesis, as well as perhaps a decrease in survival rate.6,25 27 Several other factors should be considered in the choice of type of valve prosthesis (see Section 11.1). Ultimately, the choice of mechanical versus Table 22. 