Updated June 2026
It’s a question we hear often:
Do cats really need heartworm preventatives?
The answer isn’t as straightforward as many people think.
Unlike dogs, cats are considered an atypical or imperfect host for heartworms. Their bodies are naturally less hospitable to the parasite, which means heartworms have a much harder time surviving and completing their life cycle in cats.
But “less likely” does not mean impossible.
Cats can absolutely become infected with heartworms, and when they do, the disease can look very different than it does in dogs.
As with many aspects of feline health, we believe the best decisions are made when cat parents understand both the risks of the disease and the risks of the available treatments and preventative medications.
How Do Cats Get Heartworms?
Heartworms are transmitted exclusively through the bite of an infected mosquito.
Because mosquito populations vary significantly depending on climate, geography, and season, a cat’s risk of exposure can vary dramatically depending on where they live.
When a mosquito bites an animal already infected with heartworm, it can pick up microscopic heartworm larvae. Those larvae develop inside the mosquito and can then be passed to another animal through a future bite.
Heartworm Disease Is Different in Cats Than It Is in Dogs
Dogs are the natural host for heartworms.
In dogs, heartworms can mature into adults, reproduce, and complete their entire life cycle. Some infected dogs may accumulate dozens of adult worms.
Cats are different.
Most heartworm larvae that enter a cat’s body never reach adulthood. Many infections are naturally eliminated by the cat’s immune system before the worms fully mature.
This is why a strong immune system is the first and best defense.
If adult worms do develop, cats typically carry only 1-3 worms.
Unfortunately, even a small number of worms can cause significant problems.
The immature worms can trigger inflammation within the lungs and blood vessels, leading to a condition known as Heartworm-Associated Respiratory Disease (HARD). In some cases, respiratory symptoms may occur before the worms even reach adulthood.
This is one reason feline heartworm disease can be difficult to diagnose and understand.
Symptoms of HARD can look a lot like asthma, bronchitis, or even allergies. They include:
- Coughing
- Wheezing
- Increased respiratory rate
- Respiratory distress
- Some cats may also vomit and become lethargic.
Why Do Veterinarians Recommend Heartworm Prevention?
Many veterinarians recommend heartworm prevention because there is currently no approved treatment to eliminate adult heartworms in cats.
While dogs can receive medications designed to kill adult heartworms, those treatment protocols are not safe for cats.
As a result, feline heartworm management often focuses on a correct diagnosis, monitoring the cat, controlling inflammation, supporting respiratory function, and allowing the worms to die naturally over time.
Veterinarians who advocate for prevention typically point to several concerns:
- Even a single worm can cause inflammation.
- Heartworm disease can be difficult to diagnose in cats.
- Many infected cats show respiratory signs that can mimic asthma or bronchitis.
- There is no approved adult heartworm treatment for cats.
- Indoor cats can still be bitten by mosquitoes that enter the home.
While we understand why many veterinarians recommend prevention, it’s important to understand what prevention looks like. What treatments are used? How often? What about side-effects?
Understanding the Risks of Heartworm Preventative Medications
Currently, the only heartworm prevention treatments are insecticides or parasiticides. Revolution Plus, Nexgard Combo, Bravecto Plus, and Advantage Multi. All treatments, except Advantage Multi, are part of the isoxazoline drug class. The FDA received so many reports and complaints about this drug that it issued a warning on its own FDA-approved drug.
Advantage Multi active ingredients are neonicotinoid insecticides and macrocyclic lactones.
All the above treatments are topical, spot-on treatments – with chemicals absorbing into the tissue and bloodstream, and/or having lasting effect for about 30 days. Advantage Multi also includes imidacloprid, which spreads across the cat’s entire skin surface within 24 hours of application.
As you may already assume, heartworm preventatives carry potential risks and side effects.
Mild side effects may include:
- Vomiting
- Diarrhea
- Decreased appetite
- Temporary lethargy
- Mild skin irritation at the application site
- Excessive drooling if a topical product is ingested
More serious reactions have also been reported and may include:
- Tremors
- Uncoordinated movement
- Agitation
- Disorientation
- Seizures
- Severe allergic reactions
- Death
Because every cat is an individual, it is important to discuss potential risks and benefits with your veterinarian before agreeing to these treatments.
Why Some Cat Parents Choose Not to Use Preventatives
Many cat parents, particularly those who prefer a more holistic approach, choose to carefully evaluate their cat’s individual level of risk before committing to routine medication that can cause side-effects.
Some factors they may consider include:
- Whether their cat is strictly indoors
- The length of mosquito season in their region
- Local heartworm prevalence
- The cat’s age and overall health
- Previous medication sensitivities
- Their desire to reduce unnecessary chemical exposure
These cat parents often focus on minimizing mosquito exposure while supporting overall health and resilience.
It’s important to understand that choosing not to use conventional preventatives does not mean ignoring the risk of heartworm disease. Rather, it reflects a different approach to managing that risk.
Natural Ways to Reduce Mosquito Exposure
If you choose not to use conventional preventatives, reducing mosquito exposure becomes especially important.
Mosquitoes breed in standing water, so reducing mosquito-friendly environments around your home can help.
Consider:
- Emptying standing water whenever possible
- Using Mosquito Dunks in standing water that cannot be removed
- Refreshing bird bath water frequently
- Keeping gutters clean
- Maintaining proper pool circulation
- Removing containers that collect rainwater
Many cat parents also choose natural mosquito-repelling products as part of their overall strategy.
Supporting Your Cat’s Overall Health
A strong immune system is the first line of defense for preventing heartworm infection.
We believe every cat benefits from:
- A species-appropriate, moisture-rich diet
- Low-stress living conditions
- Good digestive and gut health
- Daily enrichment and exercise
- Minimizing unnecessary toxin exposure
Healthy cats are generally more resilient and better equipped to handle life’s challenges, whether those challenges come from environmental stressors, illness, or other health concerns.
What About Indoor Cats?
One of the most common misconceptions about heartworm disease is that indoor cats are completely protected.
The reality is that mosquitoes routinely find their way indoors.
While indoor cats are generally at lower risk than outdoor cats, they are not entirely risk-free.
This is why heartworm prevention remains a topic of discussion even for cats who never leave the house.
So, Do Cats Need Heartworm Preventatives?
There is no one-size-fits-all answer.
The question is whether the risk of infection outweighs the potential risks of routine medication for your individual cat.
We encourage every cat parent to educate themselves, understand both sides of the conversation, and work with a trusted veterinarian to make the decision that feels right for their cat.
At the end of the day, informed choices – not fear – are what best serve our cats.
Natural Repellent for Cats & Dogs
