Should you note your cat having an elevated respiratory rate or open mouth breathing despite being in a comfortable or climate - controlled environment, contact your veterinarian immediately. (patrickmahaney.com)
Cats with congestive heart failure do not cough like dogs or people, but often exhibit open mouth breathing and panting. (vin.com)
Open mouth breathing in cats can be a simple stress reaction to a change in environment which will subside if the stressful conditions are removed. (vrcc.com)