Heart and lung diseases increase with age and can be easily diagnosed with chest X-rays, ECG and Echocardiogram. Heart and lung medications can be highly effective, if the panting is due to heart or lung disease. Sometimes abdominal masses can be so large that they can push up against the diaphragm and cause a mechanical obstruction or compromise to the chest cavity resulting in decrease in the efficiency of the heart and lungs. Additionally, joint pain can cause increased panting. Please have your dog evaluated by a vet. Most of the problems I have listed do have medications than can improve his quality of life. Additionally, if it does turn out to be joint pain NSAIDs and acupuncture and neutraceuticals are very helpful.