What Is Heartworm Disease?
Heartworm disease is a serious condition caused by a parasite called Dirofilaria immitis. These worms are spread by mosquito bites and can live in the heart, lungs, and blood vessels of infected dogs and cats.
Even a few worms can cause major health problems, and heartworm disease can be deadly if not prevented or treated.
Heartworm disease can be found across the entire United States, but cases are much higher in the Southeast. Arkansas is one of the top 5 states with the highest prevalence.
(Source: American Heartworm Society)
https://www.heartwormsociety.org/veterinary-resources/incidence-maps
How Pets Get Heartworms
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A mosquito bites an infected animal and picks up microscopic baby worms (called microfilariae).
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Inside the mosquito, the baby worms grow into infective larvae.
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When that mosquito bites another dog or cat, it passes the larvae on.
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The larvae travel through the pet’s body and, over several months, become adult heartworms living in the heart and lungs.
Why Heartworm Disease Is Dangerous for Dogs and Cats
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In dogs and cats, heartworms can block blood flow in the heart and lungs.
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This can cause heart failure, lung disease (breathing problems), organ damage, and even death.
Signs to Watch For
Dogs
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Persistent cough
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Tiredness or reluctance to exercise
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Weight loss or poor appetite
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Trouble breathing
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Fainting, collapse, or death in severe cases
Cats
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Coughing or wheezing
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Vomiting (often mistaken for hairballs)
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Lethargy or loss of appetite
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Sudden collapse or death in severe cases
Many pets show no signs at all until the disease is advanced.
How Heartworm Disease Is Diagnosed
Your veterinarian can run simple blood tests to check for heartworm disease.
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Dogs: We look for proteins made by adult worms and sometimes check for baby worms under the microscope. This can often be done in-clinic in under 10 minutes.
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Cats: Testing can be trickier — we may use both antigen and antibody tests, and sometimes X-rays or ultrasound, but confirmation is often difficult.
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Because of the worm’s life cycle, it may take 6–9 months for a heartworm test result to turn positive after infection.
Treatment Options
Dogs
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Treatment takes several months and must be done carefully.
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Dogs are given injectable medicine to kill adult worms (melarsomine), which can be costly.
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Exercise restriction is very important during treatment to reduce complications.
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Additional medications help reduce inflammation and clear baby worms.
Cats
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There is no safe medication to kill adult heartworms in cats.
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Treatment focuses on managing symptoms (often with corticosteroids) and preventing new infections.
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Prevention is especially important for cats.
Prevention Is the Best Medicine!
Heartworm disease is completely preventable.
Give your pet a monthly heartworm preventive — available as a pill, chew, topical, or injection. These medications kill immature worms before they can cause damage.
Even indoor pets need protection, since mosquitoes can get inside homes, especially in high-prevalence areas.
Prevention Tips
✅ Give preventive medication year-round to all pets in the household
✅ Test dogs yearly for heartworms (or after a lapse in prevention)
✅ Use mosquito control when possible
Key Takeaways
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Heartworm disease is extremely serious but easy to prevent.
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Dogs and cats both need protection — indoor or outdoor.
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Monthly prevention costs far less (and is much safer) than treatment.
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Regular checkups and testing help keep your pet healthy and safe.
Give us a call or book an appointment at All Pets Animal Hospital to talk about which heartworm preventive is right for your pet. Protecting against heartworm is one of the easiest and most important ways to keep your dog or cat healthy and happy!