The last time I purchased Heartgard for my dog, it required a prescription from the vet and about $60 for a 6 month supply. This would run me $120 per year. If I had two dogs, $240 per year. In addition, I have to have a prescription from my vet. I knew there had to be a cheaper and easier way. The only active ingredient in Heartgard is Ivermectin, which is sold over the counter for livestock.