No one will ever tell you not to ever treat your ferret for heartworm. That would be completely irresponsible. However- many vets will over treat this in the same way they over vaccinate. Good article by Dr. Becker:
Ferrets: Contessa Kitties: Watson, Oskar DIP Sinnead, Vincent, Boris, Zeus and Athena, Willow, Mr. Frodo, Indie, Lucrezia, Judge, Odin, Miss Emily, Suki, Cody, Aristotle, Butterscotch, Frankenfurter. RIP Herne, Ligeia, and Mr. Stubbs