Is there anything natural you can give a dog to prevent heartworms? I've been looking online but haven't been able to find anything. Sam can't be on anything, and as a result must be tested every 4-6 months until he comes up positive and then we'd have to worry about things from there. And his next test is DUE tomorrow (but will prob. take him next week), and the these things are always nerve wracking. Or I wonder if there is something I could put on him to prevent mosquito bites? I try to limit his playtime to times of the day when mosquito's are most minimal, but it's Louisiana and it's summer, so mosquito's are pretty much 24/7 now.