
Hi, I'm a Registered Nurse, and so what I'm going to describe is my knowledge of what happens to people with Cardio- Myopathy. I have no experience of animals with this condition.
As you no doubt already know, cardio-myopathy is a disease of the heart muscle. It renders the heart incapable of pumping adequately. The muscle enlarges and becomes floppy, and does not move enough blood to keep the body adequately supplied. The backlog of fluid ends up lying in the peripheral tissues, and is seen as swelling of the limbs, pitting odaema. Fluid also collects in the lungs, and gradually the sufferer is unable to breathe properly, the fluid gets in the way of the oxygenated blood, which would normally be carried around the body by the pulmonary vein.
As you know, there are treatments available, but without that, there will quite quickly come a time when the sufferer will become breathless, with only minimal exertion and then unable to mobilise.
My only sorry suggestion is that you release your boy from this existence when he begins sliding down the slippery slope. Better a day too early than a day too late. Please don't let him suffer. Bless you all.
Dawn R.
Edited to add, even with treatment, ultimately, a heart transplant is required in humans, a choice not available to animals.