Lezlie,
While it's
technically true that a biological valve is less likely to clot, if you're taking Coumadin with a mechanical valve (and you certainly would), your chances of a thrombosis (clot) are very similar to someone with a tissue valve.
As far as a mechanical valve lasting the rest of your life: it might, it might not. Certainly the tissue valve would not be expected to. There would be at least one reoperation with the tissue valve.
I was 51 when I had my AVR, and I preferred and have a tissue valve for myself, for a variety of reasons. But if you're under 60 or so (and you certainly are), and your overriding concern is that you want the best possible chance of never having to have a valve reoperation, then mechanical is the way to go. It would also be the valve of choice if you have signs of myxomatous tissue syndromes sometimes associated with BAV (again, if you're under 60 or so).
You should look through posts and assess the concerns and difficulties of warfarin use, and its effects on your lifestyle. If those are reasonable to you (and many find that they are), you should consider pushing for a mechanical valve. After all, it is you who will live with the outcome, not the doctor, and you need to be content with your life choice.
In a twenty-year study, 76% of St. Jude valve owners had them for over 20 years. Source: J Thorac Cardiovasc Surg. 2001 Aug;122(2):257-69;
Twenty-year experience with the St Jude Medical mechanical valve prosthesis. Ikonomidis JS, Kratz JM, Crumbley AJ 3rd, Stroud MR, Bradley SM, Sade RM, Crawford FA Jr.
http://www.ncbi.nlm.nih.gov/entrez/...ve&db=pubmed&dopt=Abstract&list_uids=14688722
You might want to look over the types and brands of mechanical valves. St. Jude valves are the most common by far, but some of the newer designs seem to be quite promising in their clot-resistance, such as the On-X.
When you choose, be content with your choice, and enjoy its advantages.
Best wishes,