Heartworm Disease in Cats

As anyone who lives in Michigan knows, our weather is very variable. This means we can have a 60 degree day followed by a 20 degree day. This unpredictability puts your cat at an increased risk of heartworm.

Even inside cats are at high risk due to the fact that we leave our house, we open doors and windows. This allows mosquitos to have the ability to make their way into our home. There is no cure for heartworm disease for cats.  The only thing you can do is supportive care and put your cat on a heartworm preventive to keep them from getting reinfected with heartworms.

How heartworms are transmitted to a cat?

Heartworms are transmitted by mosquitoes. When an infected mosquito bites a cat, it deposits baby heartworms (larvae). The larvae migrate and mature for several months, ending up in the right side of the heart and the pulmonary arteries. They mature into adult heartworms about six months from the time they enter the cat.

What are the signs of heartworms in cats?

  • Coughing
  • Asthma-like attacks
  • Periodic vomiting
  • Lack of appetite
  • Fainting
  • Seizures
  • Fluid in abdomen
  • Sudden death



There are several methods used in diagnosing heartworms; unfortunately, none are 100% reliable so a combination of tests is often needed. There are two blood tests that can check your cat for heartworm. The heartworm antibody test determines if your cat’s immune system has been exposed to heartworms. A positive antibody test may indicate that an active infection is present. Cats who have had heartworms, but heartworms have died, will also have antibodies for an unknown period of time. This test is often done first to test for heartworms due to its sensitivity. The second test to check for heartworms in cats is the heartworm antigen test. This test detects the presence of adult female heartworms; this test is very specific but not as sensitive. Due to cats having a small worm burden ranging from 1-3 worms, if all the heartworms are malem the test will be negative. This does not necessarily mean your cat doesn’t have heartworms. Radiographs allows the doctor to view the size and shape of the heart. They can also allow them to measure the diameter of the pulmonary arteries. Many cats with heartworms have an increase in the size of the pulmonary arteries. However, many cats with heartworm have no abnormal findings on their radiographs,  especially with early infection. An angiogram is an x-ray study in which a dye is injected into the heart or veins and is seen as it goes through the pulmonary arteries. An ultrasound can be used to view internal structures of the heart and pulmonary arteries. In some cats, the actual heartworm can be seen.

What is the treatment of heartworms?

There is no drug approved for treating heartworms in cats. One of the drugs used for treating dogs has been used in cats, but there are potential side-effects. Additionally,   when the heartworms die, they pass through the pulmonary arteries to the lungs. This can result in sudden death.

There are two treatment options:

The first option is to treat with the drug designed for dogs, however side-effects include acute pulmonary (lung) failure and death in a small percentage of cats.

The second option is to treat the symptoms of heartworm disease and hope the cat outlives the worms. Since heartworms live in cat for about two years, several months of treatment is needed.  When cats are in a crisis, they are treated with oxygen and corticosteroids to relieve the reaction occurring in the pulmonary arteries and lungs, and if needed, drugs to remove the fluid from the lungs (diuretics). When they are stable, they are treated continuously or periodically with corticosteroids. Unfortunately with heartworm disease the threat of an acute crisis or death always exists.

Prevention is key in stopping heartworms in cats!

The American Heartworm Society recommends that all cats indoor and outdoor be placed on year around heartworm prevention to ensure maximum safety from  heartworms. Giving a monthly prevention is easy and safe for your cat and there are so many options to choose from. Heartworm disease is difficult to diagnosis, has unknown incidence, and no good treatment options available. The best way to keep your cat safe from heartworms is to protect it with a preventive.