To Mary in Wyoming: Porcine heart valves (made from pig hearts) have been used to replace narrowed and/or leaking human aortic and mitral valves since about 1965. Tissue valves eliminate the need for anticoagulation with warfarin that is required for mechanical prostheses. On the downside, they are not as durable as mechanical valves and therefore do not last as long. In several studies, by 15 years the porcine valve has failed in 30 percent to 60 percent of patients. Elevated cholesterol seems to contribute to valve degeneration. Valve failure is more frequent in the mitral than aortic position. Also, the rate of valve failure is significantly less in patients older than 65, with more than 90 percent of the valves functioning well at 10 years. Degeneration is rare in patients past 70 years old. Your choice of valve was excellent because your age  and the fact that the valve is in the aortic position make it very likely the valve will last as long as you do!
Biological vs. Mechanical Heart Valves
By: Dr. Zipes