Vicki
I don't have much information about your case, but the extra heart muscle sounds like the heart's compensation for the leaaky valve. When the valve does not close properly the heart has to pump harder because the blood keeps leaking back into the chamber. As a result of the added effort the heart muscle, like any other muscle) increases in size from use and effort.
It's not a good thing and can lead to more serious things. It needs watching, but I have known patients who lived a full life with no obvious problems.
smile