a heart murmur doesn't have to be a terrible thing. like yuk237 said, it's not uncommon for pups to grow out of them, but even if they don't, a dog with a slight murmur can live quite a long life with no problems.
boo, i'm sorry about your kitty. did you guys monitor his kidney levels while he was on the meds? enalapril is hell on the kidneys. we just had to switch my little heart diseased poodle to a different medication because her kidneys are having so much trouble.