I just brought my GSD to the vet today to get his yearly physical, hes almost 2. They did the heart worm test and it came back positive twice! I have had him on Heartguard since the day I got him over a year ago. The vet started his Immiticide treatment today. The vet also said it was a very early stage 1 and it was a good thing they found it when they found it. I don't understand how he could get Heartworms when I have him on Heartguard and have never missed a treatment. I picked Rocco up from the vet today and he has zero energy and looks like he is in a lot of pain. He has to go back tommorrow for his second dose of treatment. Has anyone had this happen to there dog? I dunno hes out of it from the treatment or if something is wrong and I need to be very concerned.