Can Indoor Cats Get Heartworm?

Can indoor cats get heartworm? If you’re like many cat parents, you probably think your indoor-only feline is safe from most health threats. After all, they’re not roaming the streets, chasing squirrels, or getting into scuffles with the neighborhood raccoons. Heartworm is a silent danger that doesn’t care if your cat spends their life sunbathing in a window or snoozing on your keyboard.

Wait… cats can get heartworm?

Yep. And even indoor cats aren’t as safe as you might think.

Let’s break down what heartworm is, how it affects cats, why indoor cats are still at risk, and what you can do to protect your favorite fluffball.

What Is Heartworm, Anyway?

Heartworm disease is caused by a parasite (Dirofilaria immitis) that’s spread through the bite of an infected mosquito. When a mosquito carrying heartworm larvae bites your cat, those microscopic larvae enter the bloodstream and begin their dangerous journey to the heart and lungs.

Heartworm disease in dogs tends to get more attention because dogs are the ideal host—meaning worms can grow to full size, reproduce, and live for years. But cats aren’t off the hook. While cats are considered “atypical hosts,” they can still get infected, and the disease can be severe or even fatal.

In fact, because cats have smaller hearts and lungs, even a single worm can cause serious damage.

So… Can Indoor Cats Really Get It?

This might come as a shock, but indoor cats account for a significant number of heartworm cases each year.

Here’s why:

• Mosquitoes get in. Even with screens and doors, it only takes one sneaky mosquito to slip inside—and that’s all it takes to infect your cat.
• Cats are extra sensitive. Cats are more prone to inflammation from even immature heartworms that die before reaching adulthood. This condition is known as Heartworm Associated Respiratory Disease (HARD) and can cause lasting lung damage.

• Most people skip prevention for indoor cats. Because many cat owners believe the risk is low, they don’t use preventive meds—leaving their cats vulnerable.

So yes, your indoor cat, sunning themselves in a high-rise apartment with zero outdoor access, can get heartworm. And no, it’s not just a fluke—it happens more than you’d think.

Symptoms in Cats: Often Subtle, Sometimes Sudden

Here’s the tricky part: heartworm symptoms in cats can look like a lot of other things—or be totally absent until a sudden collapse or death. Some of the most common signs include:

• Coughing or wheezing (often mistaken for asthma)
• Vomiting (even without food)
• Loss of appetite
• Weight loss
• Lethargy
• Trouble breathing
• Sudden collapse or death

Since cats tend to hide illness, and many symptoms are vague, it’s easy to overlook early signs or misdiagnose the problem. That’s why prevention and awareness are so important.

Diagnosis: Not Always Easy

Diagnosing heartworm in cats is complicated. Unlike dogs, where a single blood test is usually enough, cats require a more layered approach:

• Blood tests to detect heartworm proteins and antibodies
• X-rays or ultrasounds to examine the heart and lungs
• Review of symptoms and medical history

Even then, results aren’t always clear-cut. Some infected cats may test negative if they don’t have adult worms or if the worms are the same sex (which prevents reproduction and detectable levels of certain proteins).

Because of this, many cases go undiagnosed until it’s too late.

Treatment: There Isn’t One

Here’s where things get even more serious: there is no approved treatment for heartworm in cats.

Dogs can be treated—although it’s not easy, cheap, or risk-free. But for cats, the medications used to kill adult heartworms in dogs are too dangerous.

Instead, treatment focuses on managing symptoms, reducing inflammation, and keeping the cat stable while the worms (hopefully) die off naturally. Unfortunately, this doesn’t always work, and cats can suffer long-term damage or sudden death.

That’s why, when it comes to heartworm and cats, prevention is everything.

Prevention: Simple, Safe, and Smart

The good news? Heartworm disease is almost entirely preventable with a monthly medication.

There are several options for cats:

• Topical treatments applied to the back of the neck

• Oral medications (if your cat tolerates them)

These preventives work by killing off any heartworm larvae that may have been introduced during the previous month—so even if your cat was bitten by an infected mosquito, the medicine stops the disease before it starts.

And yes—your indoor cat should be on prevention year-round. Mosquitoes don’t always disappear in winter, especially with indoor heating, and climate change has made mosquito season longer in many areas.

Prevention is affordable, easy to administer, and often comes bundled with protection against other parasites like fleas and intestinal worms. It’s a tiny price to pay for keeping your cat safe.

Common Myths (and Why They’re Dangerous)

There are a lot of myths surrounding the question, “can indoor cats get heartworm.” Let’s clear up a few of those now:

“My cat doesn’t go outside—why would they need heartworm prevention?”
Because mosquitoes do come inside, and one bite is all it takes. Indoor cats are still at risk.

“Heartworm isn’t common where I live.”
Heartworm has been diagnosed in all 50 states, and cases are rising in many areas due to warmer weather and increased mosquito populations.

“I’ve never known a cat with heartworm, so it can’t be that big of a deal.”
Heartworm is underdiagnosed in cats due to the difficulty of testing and the vague symptoms. Just because you haven’t heard about it doesn’t mean it’s not happening.

Better safe than sorry is the best practice when it comes to keeping our fur babies healthy. A monthly medication will ensure your cat is safe from Heartworm.

Peace of Mind with Pet Insurance

Caring for a cat means preparing for the unexpected. Even with prevention, health issues can pop up—and heartworm-related diagnostics, emergency care, or long-term management can be costly.

That’s where pet insurance comes in.

Many pet insurance plans cover:

• Diagnostic tests (like x-rays, ultrasounds, and blood work)
• Emergency care
• Specialist visits
• Chronic condition management

Some even offer wellness add-ons that help cover the cost of monthly preventives. Having coverage can give you peace of mind and help you make the best decisions for your cat’s care—without worrying about the price tag.

Final Thoughts

Can indoor cats get heartworm? Your indoor cat may be living the good life—cozy, pampered, and safe from many dangers. But heartworm is one threat that can sneak in unnoticed. The best way to protect your cat? Monthly prevention, annual vet checkups, and staying informed.

And don’t forget: pairing that care with a solid pet insurance plan can help ensure your cat stays healthy, happy, and covered—no matter what life (or mosquitoes) throws your way.

So give your cat an extra cuddle today… and ask your vet about heartworm prevention and insurance options. Because keeping them safe starts with staying one step ahead.

References:

1. https://todaysveterinarypractice.com/parasitology/feline-heartworm-disease-separating-fact-from-fiction/
2. https://www.heartwormsociety.org/heartworms-in-cats
3. https://vcahospitals.com/know-your-pet/heartworm-disease-in-cats

 

Disclaimer

The information contained on this blog is intended for informational and educational purposes only and should not be construed as medical advice. It is not a substitute for professional veterinary care. Always consult with your veterinarian before making any changes to your pet's health care or treatment plan.

The authors of this blog are not veterinarians and do not claim to be experts in pet health. The information provided here is based on our own experiences and research, as well as information from reputable sources. However, we cannot guarantee the accuracy or completeness of this information.

We encourage you to do your own research and consult with your veterinarian before making any decisions about your pet's health.