Heartworms are among the most dangerous parasitic worms that infect dogs. Each year, over one million dogs are estimated to be infected with heartworms.5 The disease is passed from infected dogs to other dogs by infected mosquitoes.

Dogs become infected when bitten by mosquitoes carrying microscopic heartworm larvae. These larvae are deposited on the pet as a mosquito feeds and quickly penetrate the skin to begin their migration into the pet’s bloodstream. Eventually, adult heartworms can grow to ten or twelve inches in length and make their home in the right side of the heart and pulmonary (lung) arteries. There, the presence of heartworms leads to arterial and lung disease and in some cases, heart failure.


All dogs are potential targets for heartworm disease. In fact, canine heartworm disease has been detected in all 50 states.6

Clinical Signs of Heartworm Disease

Although some dogs with heartworm disease don't show any outward signs of illness, an infected dog may cough or wheeze occasionally, and may seem unusually tired and unwilling to play. These signs of heartworm disease can easily be missed, and may be mistaken for something else. The best way to tell if your canine patient is suffering from heartworm disease is to perform a heartworm test.

Treatment of Heartworm Disease

Treatment for heartworm disease is difficult, expensive, lengthy and may be a traumatic experience for the dog and owner. Dogs receive a series of arsenic-based shots to kill the worms and must spend up to 6-8 weeks in an environment that will not tax the dog's heart and lungs any further. This may call for crating the animal to limit activity and prevent overexertion.

Prevention of Heartworm Disease

For your patients' continuous protection against heartworm disease, it's important to recommend regular monthly use of a preventive like HEARTGARD® Plus (ivermectin/pyrantel). Lapses in compliance could give mosquito-borne heartworm larvae the small window of exposure they need to infect a dog.

HEARTGARD® Plus (ivermectin/pyrantel) is indicated to prevent heartworm disease and for the treatment and control of two species of roundworms (Toxocara canis, Toxascaris leonina) and three species of hookworms (Ancylostoma caninum, Uncinaria stenocephala, Ancylostoma braziliense).

5 Heartworm prevalent in South, expanding in other hot spots. American Veterinary Medical Association. 2020. https://www.avma.org/javma-news/2020-08-01/heartworm-prevalent-south-expanding-other-hot-spots. Accessed August 1, 2022.

6 Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in Dogs. American Heartworm Society. 2020. https://www.heartwormsociety.org/veterinary-resources/american-heartworm-society-guidelines. Accessed on August 1, 2022.