mary,
thanks for the post.
The mortality and morbidity clearly vary by the experience of the medical center and experience of the surgeon and the valve needing replacement.
Since I'm unclear which valve you are referring, I've included a link to our center's outcomes which are available on the web:
http://www.clevelandclinic.org/heartcenter/pub/about/surgoutcomes/default.asp?firstCat=59&secondCat=440
Other centers should have similar data for your perusal.
good luck