There are many reasons why a kitten might breathe heavily, some serious and some not. Only a vet can properly diagnose the problem and provide the necessary treatment.
Here are some general signs that your kitten needs urgent veterinary attention:
* Difficulty breathing
* Rapid breathing
* Blue gums
* Lethargy
* Loss of appetite
Please don't wait to seek help. A veterinarian can help your kitten get the care they need.