My Jersey (RB) had a heart murmur. He lived to be seven and I believe he died of heart failure but I can't be sure as he passed in the night. The major expense was actually diagnosing his problem. It cost us $900 to have....get this..a catscan! He had additional health problems like allergy to flea bites and chronic broncitis. Those were more expensive to deal with as he was in an oxygen tank several times and took steroids to alleve his breathing. The only thing we were told to do for the murmur was to give him half a St. Joseph's childrens asprin every day. Other than that,the vet told us it wasn't life threatening.
I agree with previous posts and talk to your vet. While I wouldn't say not to adopt this baby, just consider the additional stress and sorrow if something did need expensive vet care. Consider your situation and follow your heart.
Claudia