Why is my kitten panting like a dog after playing? Is smoking a cause?

To me, this doesn't sound like allergies. I'm concerned there could be something wrong with Fuji's heart, but don't freak out at that because I can't say for certain without seeing him in person. I'd take him back into the vet for this behavior. Best of luck.

Your kitten will need to have an exam by your veterinarian. She could be suffering from a congenital malformation of the blood vessels near the heart or have a hole in the septum of the heart. This would often not show when the kitten is resting, but when it exercises, runs and plays there is not enough oxygen being pumped to the lungs and muscles because oxygenated and used up blood mixes. Problems often do not occur until 3-4 months of age. Please make an appointment with your vet for an exam.

Sorry to hear Valak seems to have problems when playing. I would recommend taking him in to your veterinarian to have his heart and lungs checked. Some young cats can have an underlying congenital heart or lung problem that can lead to exercise intolerance. We also can see cats develop asthma and present like this too, so he may need x-rays of his chest to see how his lungs look and possibly need medication. Hopefully he is normal, but if he can't seem to play very long, I would recommend getting him checked out.

You're right that it can be normal to see short periods of panting after active play or other exercise, especially in young cats. But, this can also be a sign of heart disease or other problems. If your kitten sometimes pants, it would be best to have him examined be a vet to make sure that his heart and lungs are normal. If no problems are found, then you'll know there is no need to worry :)

I would definitely be concerned about this. Without actually seeing the incident or knowing a little bit more about your kitty, it's difficult for me to tell you what this might be. That being said, what you are describing definitely sounds like episodes of feline asthma or some other inflammatory / obstructive pulmonary condition. If your kitty is an older individual, the chance that this is something more harmful like a respiratory cancer or infectious process would be higher. In very young kittens, I would always suspect upper respiratory infection over any thing else until proven otherwise. An x-ray is usually good enough to diagnose feline asthma though in some cases it can prove challenging. Hope you and your vet can figure things out. In the meantime, I would tune down the playtime.

If he was really racing around after the toy last night, more than usual, it could explain his exertion, however, it wouldn't be a bad idea to get him in to see your vet for an exam just to be safe. You said Obi is a big cat, so there may be some Maine Coon in his background, and they have a greater risk for some heart conditions.

No, it's not normal for a cat to pant like a dog. Cats typically do not exhibit open mouth breathing, and it's a sign of respiratory distress. It could be Gus may have a heart problem causing this open mouth breathing after he plays, but without seeing him in person I can't say for certain. I would have him seen by a vet for a physical exam, routine blood tests, urinalysis, and chest x-rays. These tests will help the vet identify if the does have a heart condition causing his symptoms. Should one be found, the vet can discuss treatment options with you.