Read this ad on preloved.
http://www.preloved.co.uk/fuseaction.../010c206e.html

Obviously VERY sensible to give the dog up - but he quotes
Apparently many cavaliers suffer with this problem but as you can now understand it would be fool hardy and irresponsible to continue to breed from him.
..Apparently?!? Surely a breeder should know the basics off heart murmurs and MVD!!