Cats are not open mouth breathers.
If they have their mouth open and “panting like a dog” they are either in severe respiratory distress or very stressed.
Cats do not handle not being able to breathe well. If stressed your usually quiet cat will become viscous if it feels it can no longer breathe. Handle with Care!
Cats are prone to a number of conditions that can cause respiratory distress. Cats in fights, with heartworm disease, with bronchial asthma, or with paralysis tick poisoning can all have breathing difficulties.
If your cat appears to be having trouble breathing, please call your vet.