Heartgard is a prescription only flavored chewable for your dog to treat heartworms and roundworms and hookworms. The chew is a once a month treatment and should be used year-round for prevention. It is known for its effectiveness and as one of the tastier heartworm medications because it is real-beef flavored. Heartgard does have possible side effects but they are rare in nature and include dilated pupils, reduction in body weight, tremor-causing, and possible death. Heartgard is only prescribed to dogs and not intended for cats or horses. There are four different weight categories for dogs up to 25 lbs., 26-50 lbs., 51 -100 lbs., and over 100 lbs. Active ingredients include Ivermectin and Pyrantel. Help your dog fight against heartworms with Heartgard. Save with Heartgard coupons here.