How to make them stop playing so hard

Okay. So Harvey (8 months) and my newest addition Danny (7 months) are the very best of friends. If they're awake, they're playing.

Now Danny has some breathing issues that I'm trying to get worked out, so I know that's part of it. But every time they get riled up, it ends with both of them panting and refusing to stop playing to catch their breath. It takes Danny about 3 minutes of hard playing to start panting and Harvey about 8 minutes. And because of Danny's breathing issues it really worries me. It takes him a good 5 minutes to be able to breath normally. This is a multiple times a day occurrence.

So my question is, what, if anything, can I do to stop this? Literally, anytime Danny is awake or not cuddling with me he's trying to play with Harvey. When Danny or Harvey start panting I'll take one and put him in the bedroom, but of course Danny is on one side of the door and Harvey on the other, both yowling for the other one. And the minute I let them out, they're at it again. If I don't stop them from playing, they'll go at it until they both just fall out from exhaustion (after about 15 minutes of high speed chase).

I know they're still young and have energy to spare. But them panting all the time can not be good. Especially when they refuse to stop even when they're both panting. Any tips?

Have you asked the vet about this? If they are anything like humans, this could actually be a good thing....... working out for a stronger heart??
I don't see how that can be a bad thing... but again, I am not a vet, and I strongly advise you consulting one.

I agree to seek a vets advice since Danny has breathing issues. If you watch children play, they do sort of the same thing, run like mad till they almost collapse. (I vaguely remember having that much energy at one time in my life) Kids with breathing problems forget sometimes, because it is so much fun to run and play! They of course can get their inhalers, is there some sort of similar device for cats?
Sorry, this has been no help really.

I'd also say ask the vet. If it really is causing a problem for Danny, a loud clap and stomping feet might be in order to stop it when things get too rough and you don't want someone to get hurt. If nothing else works, a squirt bottle should stop them

I've been trying to sort out Danny's issues, via many vet visits. Xrays reveal nothing...thought maybe allergies but no meds have helped...now we're thinking possibly asthma? But usually you can see inflammation on xrays with asthma. So, for the moment both I and his vet are taking a kind of wait and see approach. Just started him on some more meds....so.

I just don't want to stress his lungs/sinuses if there is indeed something wrong and it isn't just his weird make up. And now Harvey is starting to pant, but I know his is simply because he's playing too hard. I don't know. Cats panting just sends off alarm bells in my head, lol. I've never ever had this problem before. And maybe it's doing no harm at all. I'm just being a worrisome meowmy. I'm sure you can all relate.