http://pets.webmd.com/cats/abnormal-breathing-catsPanting is not normal in a cat,
Panting is a normal process after exercise. It is one of the chief ways in which a cat lowers her body temperature, as water evaporates from the mouth, tongue, and lungs and warm air is exchanged for cool. Cats also cool themselves by licking their fur and by perspiring through the pads of their feet. When panting is rapid, labored, and accompanied by anxiety, heat stroke should be considered. Some cats will pant and breathe with an open mouth when they are frightened.
I recommend talking to your vet as well, if there are several occasions when your kitten pants. There could be a variety of reasons (heat in the summer, rambunctious play, even heart conditions, as some have mentioned).I clicked on the 2nd page and it took me a few seconds to remember I started this thread,
As I'm here, an update. Dory pretty much stopped panting after the cardiology visit. The cardiologist did mention that some kittens pant...and grow out of it. Luckily, that seems to be what Dory experienced. Having said that, I definitely recommend a vet check if your cat pants to be on the safe side.