My buddy may be dying

Thanks for all the replies and suggestions, just came back from the emergency vet hospital, just have to get him there.
He went through a heartworm routine some months back and they told me the heartworms had already damaged his lungs, he's really not supposed to exert himself to much, but i have seem him run and bark at people and trucks.
I might have two people coming over to get him in the truck, we'll see.
Thanks again all.