He won't suffer long with CHF, and it is not really "suffering" as we know it. He will just tire easily, get winded quickly, gradually lose condition and then probably just drop dead one day. Sorry to put it so bluntly. Roos have an increased risk of heart-related issues just like any other male, and big boys have an even greater risk than your smaller guys. I would not put him down unless he is actively ill. Heart problems don't really cause too much problem for chickens except that they kill them younger. It's usually a pretty quick death, though. You may have heard the term "flip" or "flipover"? It is a term that is often used when discussing CXs, and it refers to sudden deaths, generally heart-related. The CX is walking around without a care in the world when it suddenly flips over onto its back and dies. It is heart failure. And it is very sudden and quick. There may be a few seizure-type movements in between the flip and death, but that's it and that is probably just reflexive movements that don't mean anything.
I hope this helps. Good luck.
