Before people start rushing out and putting their ferrets on heartworm preventatives, here are some additional sites for information. Heartworm preventatives are poisons, and should not be given without careful thought. Please find out the actual mosquito season for wherever you live so if you decide to give heartworm preventatives you will only during that time. And one thing most vets won't tell you is that you can give it every 6 weeks and not monthly which would be less poison. It's just easier for most people to remember once a month then to figure out every 6 weeks. I haven't found any statistics directly related to ferrets, so this info is all based on dog reactions and deaths from heartworm preventatives. Life cycle of the heartworm and what must transpire for the pet to contract it: http://www.bullovedbulldogs.com/gpage.html FDA adverse reactions reports from 1987-2000: Heartgard Chewables (Ivermectin) 134 dogs died; 1033 had some type of reaction Filaribits Plus 128 dogs died; 187 reacted Interceptor (Milbemycin) 67 dogs died; 460 reacted A vets article that may get you thinking: http://www.homeovet.net/content/lifestyle/section4.html Please weigh all the risks before you make any decision either way. ~Amy~ [Posted in FML issue 5220]