Cat Heartworm

"Cats are not a natural host, with cat heartworm (FW) cases somewhat uncommon. It is contracted from mosquito bites after the same mosquito bit an infected dog. Symptoms include difficulty breathing, vomiting, and diarrhea. Most clinical signs are related to problems with lung function. Treatment options are limited for this serious condition. It is estimated that in the United States 12% of cats are exposed to the disease, with outdoor cats being at a greater risk. Cats can develop clinical symptoms after being exposed to heartworms (Dirofilaria immitis) without any heartworms being present in the cat. This is called HARD or heartworm-associated respiratory disease. HARD has symptoms such as difficulty breathing, coughing and rapid breathing (tachypnea). Since cats exposed to heartworms can develop lower airway and lung clinical signs (LA/L), it is recommended that cats in areas where there is a prevalence of heartworm disease receive a monthly preventative medication."

Heartworms in cats live in the pulmonary arteries (arteries going to the lungs) and in the heart itself.

Getting Cat Heartworm Disease

Cats are unlikely hosts for heartworm. They get heartworm disease if bitten by an infected mosquito who transfers parasitic worm larvae into the cat's tissue after biting an infected dog. The larvae or parasites hatch, turn into worms and then travel up a vein into the heart. The disease is serious since the cat has a small heart so only 1 to 2 worms can cause serious injury.

There are four factors that will affect how your cat reacts to heartworms:

  1. Number of worms
  2. Health of your cat's immune system
  3. Length of time your cat has the worms
  4. How active your cat is
Cats that are active tend to get a more severe case of heartworm disease than inactive cats.

Heartworms in cats tend to be smaller than those in dogs and have a shorter lifespan (2 to 3 years). The worms can live 1.5 to 2 years in a cat.


Heartworms in cats symptoms start when the larvae enter the pulmonary vessels in the lungs, causes a reaction in 3 to 6 months after infection.

There are few symptoms of feline heartworm. Symptoms include:

These symptoms often go unnoticed or are attributed to other causes and are not recognized as signs of heartworm.


There are several ways to diagnose feline heartworm disease.

There are two types of blood tests that can be done. One looks for antibodies, which means the cat's immune system has been exposed to heartworms. The worms may be living or dead. The other blood test looks for antigens. It detects the presence of adult female heartworms. Both tests are used together to look for heartworms.

X-rays are also used to look at the size and shape of the heart and pulmonary arteries. The arteries often come to an apparent blunt stop near the lungs where they are clogged with worms.

An ultrasound can show a better picture of the arteries, and can often even show the worms themselves.

Heartworm Treatment For Cats

Cats with heartworm are placed on a monthly preventative and short-term corticosteroid therapy (prednisone) to manage respiratory signs of heartworm disease.

The only other option is to treat the symptoms of cat heartworm disease and hope the cat outlives the heartworms. Heartworms live about two years, so several months of treatment will be required. When cats are in a crisis, they will be treated with oxygen, corticosteroids to relieve the reaction that is occurring in their pulmonary arteries and lungs, and if necessary, drugs to remove fluid from their lungs (diuretics). There will always be the threat of an acute crisis or sudden death.

Feline Heartworm Prevention Medications

Because exposure to heartworms leads to respiratory symptoms, speak to your vet to see if a preventative is strongly recommended in your area, or if your region has a high incidence of heartworm. There are three cat heartworm medicines you can buy that have FDA approval for use in preventing heartworm parasites pet cats. Ivermectin is provided in a chewable formulation (Heartgard brand), milbemycin as a flavored tablet (Interceptor brand) and selamectin (Revolution brand), a broad-spectrum parasiticide, comes in a topical formulation.

Cats that live in the southeastern and upper midwestern areas of the United States should consider the use of a preventative.



Claws and Paws Veterinary Hospital

Feline Heartworm Disease
Atkins, Clarke E. DVM

Cats versus Heartworms: How Real Is the Threat?J.K. Levy
College of Veterinary Medicine
University of Florida

Feline Heartworm Disease: State of the Art 2007
C.E. Atkins
College of Veterinary Medicine
North Carolina State University


From Cat Heartworm to Cat Health Guide Home