Cats pant after exercise to cool themselves. When cats pant, the warm air from the lungs leaves the body and water evaporates from the mouth and tongue, lowering the cats body temperature.
Other ways cats cool themselves after exercise include sweating through the pads of their feet and licking their coats.
Panting might also be a sign of heat stroke if breathing is labored and rapid or the cat is showing signs of anxiety. If the cat's owner suspects heat stroke, he or she should contact a veterinarian and attempt to cool the cat by applying cool water to the neck, groin and armpits and placing the cat in front of a fan.
If the cat is wheezing or its breathing is noisy, it might indicate feline asthma, a respiratory infection or a tumor or foreign body blocking the airway.