I don't have any direct experience. You can google - heart murmur feline - and lots of info comes up.

Some sites say young kittens will have a heart murmur their first vet visit and 6 months later it is gone and no one really knows why. So that may apply to Neko.

Some cats live into their teens with no other symptoms or problems, other do develop other symptoms which are then treated (the symptoms, not the underlying issue).

I will give you this link, it is for a feline heart group on Yahoo. It came up on page 5 of my google search, so not eay to find. You may want to browse through that or even join and ask your question.

http://ca.geocities.com/[email protected]

Good Luck!
Sandra