A normal cat should always breathe with small movements of its chest. If your cat's sides are moving a large amount, this can indicate labored breathing. Unlike dogs, cats should generally never pant. You can also try to watch for any increased abdominal movements with your pet's breathing. If you cat is breathing normally, you shouldn't see any excessive movement in the abdomen, or any hitch to the breathing.
Rapid breathing (tachypnea) is a respiratory disorder characterised by abnormal breathing that is rapid and shallow.  It is caused by a reduced level of oxygen, mechanical disorders (where the lungs aren’t able to expand as they should, usually due to a build-up of fluid in or around the lungs), and physiological disorders in which the cat’s respiratory centre in the brain is over stimulated.