He doesn't look fat enough from his photos to cause an issue but file that one in the back of your head. Losing weight will make a pretty good difference in pain control too....a few pounds isn't alot to you and me but you're talking about a five or six pound dog there. Heartworm is definitely something to think about......can have for quite awhile before issues become apparent. I would think it would be something your vet would have tested for.

When you do notice the breathing problems? Excercise? Sleeping? Gulping down dinner? Does it come in cycles and then disappear? Does it seem to match when he is in pain?

One thing to keep an eye in his heart rate. You can put your ear to his chest or even better.....but a (cheap) stethosope and keep it on hand. Normal heart rate in a dog that size is about 100-150 beats per minute. If he's playing or expending energy I wouldn't be upset about 180.....for short periods. Anything over 200....time for vet.....immediately. (so would anything under 60 in that dog)...an increased heart rate would be one of the things you would see immediately if he were struggling for oxygen. It's also a good indication of pain......you will see it rise when they hurt.....but not to 200 unless they are really in agony. Check his a lot at rest so you know what his normal is.

When he has breathing episodes.....watch carefully. DOES he have respiratory effort? If so....vet. If he IS having respiratory effort....is it on inspiration (inhaling) or expiration (exhaling).

Learn his normal gum color (pink) (also called mucous membranes...mm;s) look at them all the time....you will soon know what normal is for him....then check it when he acts ill. Signs of off gum color usually start with light pink and go to gray, then blue. I don't even like to see light pink in a dog but grayish or bluish tones signify IMMEDIATE emergency as he will would not be receiving enough oxygen to survive for very long.

Also check the "crt" capillary refill tiime. With your thumb push a bit on his mm's and see how long it takes for the blood to return to a normal color in the gums. It should take no more than a second to a second and a half.....slow refill time indicates reduced blood pressure and is NOT normal.

The trick in my opinion is not what you can do for you dog at home.....it's learning to recognize where responsibility for the animal's health ends for you and becomes time for your vet. Some of these hints will help you pick out the signs that tell you it's time for the doctor....and not just watching him at home. The more you know about your munchkin.....the more it well help his doctor. Then the more you both can work together for him.

Vets are afraid of owners I think because too many people misinterpret the signals that the animal gives out when ill...(remember...animals hide illness....natures way) ..if your vet can trust YOUR judgement about your pet you'll find there will be alot less issues between the two of you....(tests...more tests....lots of returns to the vet office....different meds......) ..which can only be good for Powder. :thumbsup: