thanx you for all the heartworm info. I'm happy with the ivermectin regime I had used and will stick with that for now. ivermectin only lasting 18 days in the system is what my vet at a university hospital told me, and I can't confirm that other than there are a number of google references saying that ivermectin should be stopped being administered to cattle at least 18 days before slaughter (yeah, a morbid reference). someone kindly pointed out that while there's a 6 month window to kill heartworm larvae, in ferrets, larvae can become a problem because of their size. so I'll definite stick with a monthly regime. another fml'er linked me to a fhl post on heartworm - http://ferrethealth.org/archive/FHL5785 many thanx. Selina [Posted in FML 7388]