I have a question about heartworm, regarding my roommate's dog, which would be this sexy beast right here: IMG_0673 by Traveling Koolie, on Flickr Ok, so Balto was pulled from a high kill shelter in May of 2011 and treated for heartworm with Immiticide on July 8-9. I don't know what his worm load was like. He's been on Heartgard ever since his treatment. Flash forward to today, and he just got a heartworm test. His old vet who ran the rescue he came from said that he would likely test positive up to a year following his treatment, but my vet today gave my roommate the impression that he would be concerned if it did, indeed, come back positive. I believe his exact language was, "The treatment can fail and if the test comes back positive, we'll have to confront that." So, what do you guys know? I trust this vet, but I'm confused by the contradictory information between him and Balto's old vet. I'm asking this for my roommate so she doesn't find scary information on the internet and work herself up over nothing.