
I lost my darling boy this year due to, amongst other things but mainly, heart failure.
He was diagnosed around 11 months before he passed with cardiomyopathy, different to your Brother and SIL's dog as my Murf had all 4 leaking valves, not significant enlargement. I noticed that he was getting very tired when out on our walks and his tongue had a blue tinge.
He was on vetmedin and fortekor for the last 11 months but we did have a few relapses and thought that we were going to lose him 3 months before we actually did. He was very thin, no matter what we fed him and he went from 50 kilos down to 43 kilos in that time but still loved his life.
We were told to keep exercise to a minimum and no more walks, just let him wander around the garden. We had a heart monitor jacket put on him for 24 hours to monitor his heart beats. My vet told me that if he over exerted himself he could just drop. It was hard telling Murfee that though as he still wanted to leap about for short periods of time, but I didn't dare take him out for a walk as where we live, in the middle of nowhere, if we went 15 minutes up the road and he took a bad turn, I was worried about getting him home again.
I would say that restricting his exercise is sensible but other than that, let him enjoy his life and be there for him to make the right decision when the time comes. My old boy collapsed one morning, we took him to the vet and they decided to change his meds, when we went to leave, he collapsed again and I knew from the look in his eyes that he couldn't cope any more, he was tired of living with it. That particular day he was also refusing all food which I knew was a sure sign, as all of his life, he loved his food.
I hope that they have more time with him yet and that they all enjoy the time that is left