I use interceptor and frontline plus. The proheart6 injection cost the same as the interceptor but does'nt cover the intestinal parasites. Do beware of buying heartworm preventative over the internet. yes it is cheaper but if your dog gets heartworms and you have been buying it over the internet, the companies will not guarantee it. If purchased from a vet, Phifzer, Norvartis, and Merical will pay for the treatment to get rid of heartworms. I have seen dogs on heartgard, interceptor, sentinel, and revolution get heartworms and the companies paid for the treatment . It is best to have your pet tested for heartworms once a year. there is also preventatives for cats. But there is no treatment yet avaliable for cats. Although it is rare for a cat to get heartworms, every year more cases are being reported. my cats are on heartgard.