Vicky and anyone else who might be interested. Ferrets ARE succeptible to heartworm. I don't know about whether or not they are an optimum host, but I have been told by a very good ferret vet and I have read in Fox's "Biology and Diseases of the Ferret" that as few as i to 2 worms can kill a ferret where a dog can host many more and still have a chance to recover. Our ferrets don't get heartworm treatment as they very seldom go outside and we are not in a very risky area anyway. If you are in a risky area i'd suggest getting another opinion from a different vet. Best Wishes, Leigh and Fargo, Fonzi, Kami, and Moon Boy [Posted in FML issue 3088]