My story is also similar. I had no idea I had a murmur or any heart problem until I was diagnosed with severe MVR. That was in Dec of 2011, I had repair surgery on 6/4/12.
Unlike you, my kids are grown. I think that makes a difference on how much you worry. I found a really good surgeon at Yale University Hospital who did a great job and I now feel wonderful. I'm keeping up with exercise...not so great on the eating right, but I'm trying.
Read my story, let me know if you have any questions.
My story is similar to yours in that I had no idea there was anything wrong with my heart until a GI doctor heard a murmur at a routine visit. Turned out I had three bad valves, and it was quite a shocker! My advice to you is to make sure you do as much research as possible and to have your surgery done at a major heart center. Read as many journals on this site as possible and be sure to read Dave Van Buren's journal from the start. He has done a lot of research and has shared it all.
The waiting for surgery is truly the worst part. I promise the surgery won't be nearly as bad as you are imagining!
Godspeed and good luck!