Ivermectin among every Veterinarian I've dealt with, had been the foremost mode of treatment against heartworms in ferrets. Selemectin; the ingredient in Revolution ("Stronghold" abroad), in the same manner affects the neurological system of the target parasite. I have had ferrets treated with both products with no ill effects other than the possibility that the patient already having been infected with heartworms, being in risk of blockage from the dead worms. I found this article (dated 2007)from a German study. there is a table on page 7 that describes the dosage. (Sorry for the long URL) [I "simplified" it. BIG] http://www.jarvm.com/articles/Vol5Iss3/Beck%252087-96.pdf [Posted in FML 7387]