Recognizing the Signs of Heartworm

retriever dog and gray and white kitten sitting outside in the grass

Both dogs and cats can contract heartworm. Would you recognize the symptoms?

While heartworm is most commonly found along the Atlantic and Gulf coasts and the Mississippi River, it’s present in all 50 states and can affect animals year-round. Heartworm is transmitted by mosquitoes that carry the heartworm larvae. When an infectious mosquito bites a pet, the parasite enters the bloodstream and settles in the heart and lungs.

dog and cat rolling in the grass

Both dogs and cats can be afflicted with heartworms, though in different ways. Dogs are natural hosts for heartworm. The worms can mature into adults and produce offspring, resulting in hundreds of worms that invade the heart, lungs, and blood vessels. Worms can grow up to 12 inches long and live up to seven years.

Heartworm is not as prevalent in cats, though they can still cause serious health issues. Most worms don’t live to adulthood, which makes heartworm harder to detect. Cats typically have only a few worms that can live up to three years and affect the lungs and heart, causing heartworm associated respiratory disease.


Dogs exhibit very few signs during the early stages of infection. Symptoms include a dry cough, weight loss, difficulty breathing, fatigue, and decreased appetite. In the advanced stages, a dog might experience heart failure or have a swollen stomach due to excess fluid. Signs of a cat afflicted with heartworm include vomiting, diarrhea, coughing, respiratory problems, lethargy, and decreased appetite.


Prevention is critical to keeping your pet healthy. The American Heartworm Society advises pet owners to “Think 12: Get your pet tested every 12 months for heartworm and give your pet heartworm preventive 12 months a year.”

A veterinarian can prescribe a year-round preventative medication. In addition, dogs should be tested for heartworm every year. Veterinarians will use a variety of methods to diagnose heartworm in cats, including antibody screening, x-rays, or ultrasound. (There is no standardized heartworm test for cats.) The earlier heartworm is detected, the better the prognosis.