Heartworm Disease in Cats

Rare but Dangerous—What Every Cat Owner Should Know

Heartworm disease may be less common in cats than in dogs, but when it strikes, it can be devastating. Because cats are not a natural host, heartworms often cause severe immune reactions, respiratory distress, and—tragically—sudden death. Worse still, it’s incredibly difficult to diagnose and there’s no safe treatment once the worms mature.

At Whittington Veterinary Clinic, we know how serious this disease can be. That’s why we’ve answered your most common questions about feline heartworm disease—so you can protect your cat before it’s too late.

What Is Heartworm Disease in Cats?

Heartworm disease is caused by a parasitic roundworm (Dirofilaria immitis) transmitted through mosquito bites. While dogs are the primary host, cats can also be infected—even strictly indoor cats.

Unlike in dogs, where adult heartworms can thrive, cats usually mount an aggressive immune response that damages their lungs as the immature larvae migrate. In many cases, the worms die before becoming adults—but not before leaving permanent inflammation and respiratory damage.

How Do Cats Get Heartworm?

Cats become infected the same way dogs do: through the bite of an infected mosquito. Once bitten, immature heartworm larvae enter the bloodstream and travel to the lungs and heart. After several months, some may mature into foot-long adult worms. Even a single worm can trigger a fatal reaction in a cat.

Because cats aren’t natural hosts, many infections go undiagnosed—and many more go unreported due to the lack of accurate testing.

What Are the Signs of Heartworm in Cats?

Symptoms can resemble asthma or other respiratory diseases and may come on suddenly or subtly:

  • Coughing or wheezing
  • Open-mouth or labored breathing
  • Vomiting unrelated to eating
  • Lethargy or decreased activity
  • Weight loss
  • Collapse, seizures, or sudden death in severe cases

If your cat is showing any of these signs, contact us immediately.

How Do We Diagnose Heartworm in Cats?

Unfortunately, cats don’t have a reliable single test like dogs do. Instead, diagnosing feline heartworm involves a combination of testing and imaging:

  • Heartworm antibody test – Detects past or current exposure
  • Heartworm antigen test – Looks for adult female worms (often negative in cats)
  • Chest X-rays – Assess lung and heart health
  • Echocardiogram (ultrasound) – Views live worms or heart changes
  • Bloodwork – Elevated eosinophils may suggest infection
  • Urinalysis – Helps rule out other systemic issues

Diagnosis can be difficult and often occurs after significant damage has been done.

Why Early Detection Is So Important

There’s no approved treatment for heartworm disease in cats like there is for dogs. Once adult worms form, the damage is often irreversible—and the inflammation caused when the worms die can be fatal.

Because even a single worm can be life-threatening, early prevention is absolutely critical. The lung damage caused during early larval migration can result in long-term respiratory issues, even if the worms never fully mature.

What Do We Recommend for Prevention?

At Whittington Veterinary Clinic, we recommend monthly heartworm prevention for all cats, including those that live indoors. Mosquitoes easily get into homes and apartments—and it only takes one bite.

Recommended products include:

  • Bravecto Plus for Cats (topical)
  • Revolution Plus (topical)

Many of these medications also protect against fleas, intestinal parasites, and ear mites, making them a convenient all-in-one solution.

Do Indoor Cats Really Need Heartworm Prevention?

Yes. Even indoor cats are at risk:

  • Mosquitoes find their way into homes year-round in South Louisiana
  • Cats may escape outdoors unexpectedly
  • You may adopt another pet or move to a higher-risk environment
  • Rabies and heartworm prevention are considered core care, regardless of lifestyle

It only takes one bite for a cat to become infected—and without prevention, the consequences can be fatal.

Protect Your Cat Before It’s Too Late

Because heartworm is so difficult to detect—and impossible to treat once it reaches the adult stage—prevention is the only safe solution.

If you have questions about heartworm disease or want to start your cat on prevention, please call us at (337) 893-8522. We’re here to keep your cat safe, healthy, and heartworm-free.