Cavalier King Charles and BAOS?

Cavalier King Charles spaniels are more genetically prone to Brachycephalic airway obstruction syndrome because of their short head and compressed upper jaw. The symptoms you are describing sound like BAOS. Dogs with this condition may have difficulty exercising and have a heat intolerance. Your dog may also have noisy breathing, snorting, snuffing or loud snoring. They will also pant excessively which is dangerous, it can cause the airways to swell which may cause the dog to faint from lack of oxygen. What you need to do is to take care not to let your dog overheat, get overly excited or get to much exercise. Keep your dog nice and trim, don't let them get to fat because this can increase their breathing troubles. Cut what you are currently feeding him in half and split that into two separate meals, like breakfast and dinner. Death can occur if your dog is not treated for this condition. In mild cases, calming and cooling the dog may be sufficient. However, if this does not seem to relieve your dog's struggle to breath, take him to a vet. They may prescribe corticosteroids for short term relief, this will help open up the dogs airways and make breathing a little bit easier. In some cases surgery is required to correct the problem, talk to your vet about more of what you can do for your cavalier. Good luck, I hope your dog feels better soon!