From what I have read the Ivomec doesnt kill the adult worms but rather the microfilaria, the life cycle isnt complete until the mosquito redeposits it into the dog. The adult worm lives 2 years so technically if you keep them on a good dose of Ivomec your will be OK once the current worms die off.
I had a dog as a kid that was so infected the vet gave it 6 months and said dont bother treating it. We gave it heart guard for a couple years and at the vet visit the vet said it had nothin. heartworms only live two years. Start it on Ivomec every month .1cc per ten pounds and keep it up. if the dog lives long enough to let the adult heart worms finish their life cycle it will be fine. The ivomec just keeps new eggs from hatchin so to speak
