I took my three dogs to the Vet for heartworm testing. They have been on Revolution last year with the last dose given in December. The vet called today and told me he got a weak positive for on of my labs and the other lab and bichon were negative. He used an outside lab to run the tests. I took the lab to the vet today for more testing (to look for microfilariae in her blood). When he could find none in her blood, he tested her in his office for heartworm and he got a negative result. Has anyone gotten two different results from separate testing before? Should I have her tested again at another vet?? This is getting very costly, but I don't want to treat a dog who does not have heartworm. We are switching to Heartguard which is what the vet would have used to treat her if she was weak positive.