Animal Clinic of Billings and Animal Surgery Clinic veterinarians Bobbi Jo Massic, Bryna Felchle, Stew Sherburne, Christiane Youngstrom and Ken Brown

Since 1981 the Animal Clinic of Billings has made heartworm prevention an integral component of our preventive care protocol for dogs. If a dog is infected with heartworms, their presence will lead to serious cardiac and pulmonary disease that is ultimately fatal. Therefore, heartworm prevention is very important. At the Animal Clinic of Billings and Animal Surgery Clinic, our team of veterinarians and veterinary technicians are here to do everything we can to help protect your dog from this terrible disease.

What are heartworms in dogs?

Heartworms are parasites transmitted by mosquitos that inhabit a dog’s (or rarely, a cat’s) heart. Over time, as they grow and interfere with heart function, they cause heart and lung disease, which will ultimately be fatal if not treated.

In Montana, the mosquito population can vary quite a bit depending on the temperature and the amount of moisture we receive, but mosquitoes are typically present from about April through October or early November.

How can heartworms be prevented in dogs?

Heartworms can easily be prevented in dogs with medication that comes in the form of a monthly chewable tablet. We carry monthly Interceptor Plus and recommend that all dogs receive it year-round. The chew should be given once every thirty days to ensure your dog is adequately protected from heartworms. This medication also has the benefit of preventing the most common types of intestinal parasites.

Are heartworms treatable in dogs?

There is an effective treatment for heartworms in dogs, but it does have risks, and the damage that has already taken place cannot be undone. Therefore, it is MUCH better to prevent disease than to treat. Monthly preventatives are very effective in preventing any microscopic heartworm larvae introduced by a mosquito bite from surviving long enough to infect the heart.

How are heartworms treated in dogs?

While many people in colder climates only treat during the warmer months, the American Heartworm Society recommends all pets be treated year round, in order to reduce the risk of early or late-season transmission. They also recommend annual testing (in-house blood test), so if a lapse in coverage did occur, treatment can be started before the heart and lungs get damaged.

A blood test must be performed on your dog to diagnose the presence of heartworms and begin a treatment protocol. If the blood test is positive for heartworms, additional testing such as a confirmatory antigen test, a urinalysis, and chest X-rays, will then be needed to determine the severity and stage of the heartworm disease in order to properly treat it. Additionally, an ultrasound of the heart may be required for our doctors to determine the extent of any damage that has occurred within the internal structures and surrounding vessels of the heart.

If our doctors determine a dog’s heartworm disease is treatable, the patient will likely need to be hospitalized and given a medication specifically designed to kill heartworms known as an adulticide. Several treatments will be administered over a period of several months to kill the adult worms. The treatment itself has a risk of causing serious complications, but measures are taken to minimize these.

In some extreme cases, surgical removal of adult heartworms from the inner veins and arteries of the heart may be needed, but this is very rare.

Can cats get heartworms?

While it is possible for a cat to get heartworm, it is very rare, and preventatives are often only given to cats in areas where heartworm is extremely common (southern States). Effective monthly heartworm preventatives also exist for cats; the one we carry is Revolution, which is a topical medication that also kills fleas, ear mites, roundworms, and hookworms.

How can I tell if my dog has heartworms?

When heartworms are present in a dog, symptoms gradually develop with progression through the four stages of disease.  

Stage 1

The first stage of heartworm disease in dogs typically has no indicating signs or symptoms at all. During the first stage, heartworms are just beginning to establish themselves within the dog’s heart and have not begun to reproduce.

Stage 2

The second stage of heartworm disease in dogs will cause symptoms of exercise intolerance and a mild chronic cough to develop. At this point, the heartworms have established themselves in the heart long enough for the reproduction and antibody production to take place, and infection can now be detected with a blood test.

Stage 3

By the third stage of a dog’s heartworm disease, the symptoms are very noticeable and impact your dog’s health tremendously. Coughing (sometimes with blood), difficulty breathing, and reluctance to exercise all develop. By stage three, the damage to the heart caused by the heartworms will be visible on X-rays.

Stage 4

By stage four, an infected dog will be very ill and present all of the same symptoms of stage 3, only more intense. Even with heartworm treatment, this stage of the disease carries a poor prognosis.

Additional heartworm disease symptoms in dogs can include:

  • Rapid Heart Beat
  • Fainting
  • Anemia
  • Heart Failure
  • High Blood Pressure
Animal Clinic of Billings veterinarian Dr. Christiane Youngstrom

These symptoms are indicative of the advanced stages of heartworm disease. If you notice any changes in behavior in your dog that indicate potential heartworm disease, please call us right away to schedule an appointment with one of our veterinarians.


Schedule an appointment with us to ensure your dog is protected from heartworms.

Heartworm disease is easily preventable, so if your dog is not currently using a veterinarian recommended heartworm prevention medication, please schedule an appointment with us right away. Today, many ineffective and even downright dangerous over the counter heartworm remedies are available, so it’s imperative you consult your veterinarian first before making any heartworm preventive care decisions on your own.


Let our highly trained and experienced team of veterinarians and veterinary technicians help you keep your pet as happy and healthy as they can be.

Call the Animal Clinic of Billings to schedule your pets next wellness examination with us today!




providing our region’s companion animals and their families what they need and deserve since 1981

1414 10th St. West, Billings MT 59102