In addition, cats don’t have sweat glands in their bodies (only in their paws!) and can’t cool off via panting like dogs can. Their primary cooling method is via evaporation of saliva off their fur during grooming; a process that takes a bit of concentration and time and is difficult to do when they’ve already exerted themselves.
Daily interactive play sessions should be the norm for all cats and their owners – preferably at dawn and dusk to take advantage of and exercise their natural hunting drive – but you want to pay attention so you don’t push the cat so far he becomes overheated. If you see him panting, he’s already crossed the line! Ten or fifteen minutes of playtime is sufficient, and don’t spend that entire quarter hour flipping the “prey” wildly through the air and out of reach. Drag it, twitch it and hide it to simulate real prey, and let the cat occasionally catch and grapple with it. End the sessions by tossing down treats or catnip toys to simulate successful hunts. Your kitty may be too excited to quit on his own, so it’s up to you to regulate the time for him.
You can slowly increase your cat’s physical and respiratory strength by consistently and incrementally extending your play sessions, but there is a point he just won’t be able to pass. You’re better off increasing the number of play sessions and keeping the length short than exhausting him in one marathon session.