Yes, there is a dose of heartworm medication that works for ferrets.  Dr.
Williams, I think, posted it once last year based on a formula from another
vet.  It's a liquid medication.  I wonder if BIG (Bill, is this OK with
you?) would be willing to help us find the issue with this information.
 
[Moderator's note: You might be thinking of issue 1159, but note that
heartworm disease has been mentioned in dozens of past FMLs as well as in
the FAQ.  And don't necessarily believe everything you read - the suggested
dosages of preventative discussed on the FML vary by an order of magnitude.
But, that being said, the most common suggestion is oral ivermectin
solution, and if you average out all the varying dosages recommended, it
seems like we're talking about 10-20 micrograms of ivermectin per pound of
ferret.  Probably anything in that range is both safe and effective from
what I can gather - sometimes higher doses are used to treat other parasites
with no apparent ill effect on ferrets (or other mammals).  BIG]
[Posted in FML issue 1517]