I have a question. Loki just got over a bout of roundworms. I wormed him and then we went for a checkup at the vet. The vet tested for heartworm and that was negative. Loki was then put on Heartguard. That was three weeks ago. Well, the roundworms are back. I asked the vet whether I should reworm him and he said no. He said the heartguard would take care of it. Now, I know that is what the box says...but I am unsure. Anybody have and thoughts or suggestions.