When my precious little Tigger was diagnosed with HCM at 6 months of age, I told my vet I was terrified to play with him. But my vet had some wise words. He said that Tigger didn't know he was sick, and wanted to be a normal kitten. He said kitties are "here for a good time, not a long time -- so have a good time, the sun don't shine everyday". So Tigger (who is 8 now) and I play everyday -- a little exercise is actually good for his heart. He loves his mousie on a string the best, so we play with that, and he chases it around and up his cat tree, etc. I just watch him very carefully. The second I see him slowing down or breathing harder, we stop. I wait at least 10 minutes for him to catch his breath and calm down, then we play for longer if he wants to. I also throw things for him to chase the length of the hallway, even tho he seldom brings them back. The cat tree has truly helped him build up his upper body strength. When I first got it 5 years ago he couldn't get up to the little house on the top. But he worked on it, and now he just bops up there in a moment. It has definitely made him stronger.
Tigger has periods of time (sometimes for a couple weeks) when I cannot get him to play, when he just wants to lay around, and that's okay too. But when he brings me the mousie, I know he's feeling good and wants to play. I know a little exercise will only help him in the long run.
If your kitty has more serious HCM than Tigger has, or is on more meds, has history of heart failure or fluid build-up, etc -- play very gently and don't make them run or jump. But give them a chance to enjoy being a kitty for a while each day. Don't keep them in a bubble -- I think you know what I mean....
take care -- Michelle & Tigger Too in Toronto
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