I hope I am not being to blunt.  The recommended dose of Revolution for
ferrets is one tube of the 5-15 pound cat size per ferret!  This is the
dose that the company that makes it (Pfizer) recommends.  When they did a
small trial with the 0-5 pound kitten size tube per ferret it was NOT 100%
effective in preventing heartworms, but the 5-15 pound cat size WAS 100%
effective in preventing heartworms.  That is why the recommended dose is
one tube of the 5-15 pound cat size per ferret once a month.  Thus the
safe and EFFECTIVE dose is one tube of the 5-15 pound cat size monthly.
 
Hope that clears up the confusion,
Jerry Murray, DVM
[Posted in FML issue 3541]