I forgot to cat
Decided to dog.
Friendly reminder that this behavior is generally very abnormal for a healthy cat. The ONLY time a cat should pant open-mouthed like that is right after some prolonged, high activity. This cat is alert, his tongue is pink, his pupils are dialated. He/she has just been playing very hard and needs a cool-down.
If a cat that has not been playing hard is panting like that, or if their tongue/gums are pale, GET THEE TO THE VET ASAP. Do not call ahead. Do not wait until Monday. Get that kitty to the vet immediately. If your vet is closed, find the closest emergency vet. Cats panting open-mouthed are often in imminent heart/lung failure and this is a last resort to get some oxygen to their struggling organs.