Even if Chipper does test negative for heartworm, please, please get him on a preventative program asap! It's a most serious, life threatening condition that can be easily prevented. The treatment is drawn out and very pleasant Did your vet ever mention putting him on a heatworm preventative plan? I'm sure your vet will help you to figure out the cause! Please keep us updated on the coughing heartworm and teeth cleaning! Hugs to Chipper! (Do you have any pictures???)

My girls occasionally make that hacking sound, neck outstretched. But, it's usually from a small bit of debris, bit of kibble at the back of their throats that they want to clear.