This is from a web site i found
Dogs pant when they are hot, but panting can also be a symptom of an illness or a sign of stress. If your dog is panting excessively it's not a reason to rush to the emergency vet, but is definitely something to monitor.
Panting can be a symptom of lungworm or heartworm, both of which require medical treatment, but more often frequent dog panting is caused by obesity or stress. An obese dog may literally feel crushed by his weight, to learn more about helping your dog regain a healthy weight see our article on obese dogs.
We worked with one rescue dog who panted constantly for the first 2-3 weeks we fostered her. As she settled into our home the panting eventually went away.
Has your pet experienced any major changes recently? A new dog? a new family member? A new home? The answer to your dog panting problem may just be more quality time (time spent playing and keeping the dog busy, not rewarding the panting with coddling) or allowing your dog to have a "safe place" to get away on his own, like a crate with a crate cover or a dog bed placed in a closet.
If you've ruled out stress and medical causes for your dog panting, you're dog may just be "a panter".
In investigating our panting dog and consulting with vets and other dog people we heard about several dogs who, even when relaxed, healthy, and cool just panted frequently. Apparently, some deep chested dogs may pant for no other reason than it's comfortable for them.