I had a really interesting chat with my vet today about lung worm/French heartworm. Apparently Milbemax is not a preventative for French Heartworm, I have researched this and she is correct. It does treat but does not have any preventative uses MilbemaxÂ® (Milbemycin Oxime, Praziquantel) - Novartis Animal Health Inc. http://www.ivis.org/advances/Parasit_Bowman/conboy_angiostrongylosis/ivis.pdf Notice the difference in type French Heartworm: Angiostrongylus vasorum, Heartworm: Dirofilaria immitis Heartworm does not exist in this country at the moment. She also said that the drug companies have been trying to prove that the French heartworm is present in the slime of slugs and snails, but as yet they have not been able to find any. The biggest risk of a dog contracting French heartworm is through ingesting fox faeces and whole slugs and snails. Advocate is the only licensed preventive of French Heartworm.