According to WebMD, Heartgard Plus and Interceptor are the two most popular choices of heartworm medication. Heartworm is a disease that is transmitted by mosquitoes.
When an infected mosquito bites a dog, it introduces heeartworm microfilaria into the dog's bloodstream. These microfilaria invade the heart and grow into heartworms. Because the disease is difficult to treat, veterinarians recommend that a heartworm preventive protocol begin when a dog is between 6 and 8 weeks of age and continue monthly throughout its life. Oral preventives include Heartgard Plus, Interceptor and Trifexis. Revolution is a topical heartworm preventive, and ProHeart is an injectable preventive that is administered once every six months.