Dog & cat health · Vet-reviewed guide

Cat Heartworm Symptoms: Why There's No Cure and Prevention Is Everything

Most people think heartworm is a dog problem. For cats it's rarer but scarier, because once the worms arrive there's no drug that can safely get rid of them. Here's what matters before mosquito season.

Quick answer: The single most important fact about heartworm in cats is that there is no approved treatment to kill adult heartworms in cats — which makes prevention the only real protection. Unlike in dogs, the drug used to clear adult heartworms is toxic to cats, and surgery to remove worms is high-risk, so a cat that develops heartworm can only be managed and supported, not cured.

Heartworm is spread by mosquito bites, and indoor cats are at risk too, since mosquitoes get inside. Even a single worm can cause severe illness or sudden death, and it can cause a lung condition called heartworm-associated respiratory disease with coughing and wheezing that is easily mistaken for asthma. Because there is no cure, veterinarians strongly recommend year-round heartworm prevention for all cats. This guide explains the risk, the signs, and why prevention is non-negotiable.

Why this matters: There is no drug approved to kill adult heartworms in cats, and the canine treatment is toxic to them. Prevention is the only reliable protection — talk to your vet about a year-round preventive.

Why cat heartworm is different from dog heartworm

In dogs, adult heartworms can be killed with a treatment protocol. In cats, there is no FDA-approved drug to kill adult heartworms, and the medication used in dogs is toxic to cats.¹ Surgical removal is possible in severe cases but carries a high risk of death. This is the crux of feline heartworm: you cannot reliably cure it, only prevent it. There is no cure, so an antibiotic or any medicine is not always the answer here.

How cats get it, even indoors

Heartworm is transmitted by mosquito bites, not from other pets, and mosquitoes readily get indoors, so indoor-only cats are still at risk.¹ Cats are somewhat more resistant than dogs and usually carry only a few worms, but in cats even one or two worms can cause serious, sometimes fatal, disease.

The signs, and why they're easy to miss

Heartworm in cats is hard to detect and its signs are often subtle or mistaken for asthma: coughing, wheezing, rapid or difficult breathing, vomiting, weight loss, or lethargy.¹ Sometimes the first sign is sudden collapse or death. Vets diagnose it with blood tests and imaging, but detection is genuinely difficult, which is another reason prevention beats reaction.

What "treatment" means for an infected cat

Because the worms cannot be safely killed, care for an infected cat focuses on managing symptoms and supporting the cat, monitoring closely, and treating the respiratory disease, in the hope the cat outlives the worms.¹ It is management, not cure.

Prevention: the only real answer

Year-round heartworm prevention is strongly recommended for all cats, indoor and outdoor.¹ Preventives are prescription products, given monthly as a chewable or a spot-on, and many also protect against fleas and intestinal worms. A vet may test before starting them. Because there is no cure, this is one of the clearest cases where prevention is essential. If your cat needs a prescription preventive, our licensed veterinarians can review your cat and issue one when appropriate. See how our vet prescription service works.

When to see a vet

See a vet promptly if your cat has a persistent cough, wheezing, difficulty breathing, or unexplained vomiting or weight loss, and talk to your vet about starting year-round prevention regardless.¹ For mosquito-borne and other parasite protection together, see our prevention guide.