Mother Nature sent him to my door (aka: some ignorant SOB kicked him out of a car on the nearby highway & he showed up), loaded with parasites, including heartworm.
They first had to put him on doxy to kill the parasite that lives on the heartworms. (This is the reason dogs must be heartworm tested before given preventative medicine. It can kill them.)
We chose the "slow kill" method because when undergoing heartworm treatment the dog needs to be very sedate. That is not this pupper at all. LOL THe vet said he would pretty much need to be knocked out for 6 months while undergoing treatment. (If they get riled up / hyper, the heartworms can break up and aspirate into their lungs and kill them.)
All that said, I've met lots of folks at the dog park who just do the "slow kill" method, keeping them diligently on heartworm preventative and the worms die off.
Guessing the rescue already has your preferred pupper undergoing treatment though.
Good luck to you! Looking forward to another pupper joining DU! And pix, lots of pix please?