Purchasing Pet Drugs Online: Buyer Beware
All heartworm preventative meds require a perscription. Be very, very careful if you order online. Saving a dollar could be dangerous. If I were you, I would find a different vet...charging $60.00 for a six months supply is crazy! It's usually about $35.00.
I also have a thread about heartworm preventatives and I'm still waiting for responses. If your (new) vet suggests ivergard, make sure you are able to be home with him incase he has a severe reaction, like Prince did...severe vomiting, shaking and lethargy.