
Hello
Afraid I can't help, as I've not come across this personally in flatcoats. I believe it can be a secondary effect due to exposure to infection - maybe something like parvovirus.
I think it's found more often in large breed like Great Danes and Wolfhounds. There is a good site on
http://members.nbci.com/wolfhounds/health.htm linking to hearts.
If it is controlled by the drug, enjoy your dog as much as you can within the limits of his ability!
Kind Regards
Jo and the Casblaidd Flatcoats