No, a heartworm-positive dog can't directly infect a cat; both species need a bite from the same infected mosquito to get heartworms.
What are the symptoms of heartworms in cats?
Symptoms of heartworms in cats often look like feline asthma or other breathing problems
Watch for signs like throwing up (sometimes with blood), diarrhea, fast or struggling breaths, constant coughing or hacking, not wanting to eat, acting tired all the time, and losing weight. Because cats aren't natural hosts for these worms, symptoms might come and go without warning—making it tough to spot the problem. The American Heartworm Society says to get your cat to the vet right away if you notice any of these. Heartworm disease can be deadly, and cats don't show symptoms until it's often too late.
Can a heartworm positive dog infect a cat?
A heartworm-positive dog can't pass heartworms directly to a cat; both need bites from the same infected mosquito.
Heartworms need mosquitoes to spread—so just living near an infected dog won't raise your cat's risk unless you're both in an area with infected mosquitoes. That said, cats in homes with heartworm-positive dogs face the same risk as any other cat if mosquitoes are around. The American Kennel Club recommends all pets in a household stay on year-round prevention—no exceptions.
Can indoor cats get heartworms?
Yes, indoor cats can get heartworms; even one infected mosquito sneaking inside can spread the parasite.
Indoor cats are safer than outdoor cats, but the risk never disappears completely. Mosquitoes can slip in through open doors, broken window screens, or even hitch a ride on you or your other pets. The ASPCA reports that about a quarter of feline heartworm cases happen in cats that never go outside. Bottom line? Prevention matters, no matter where your cat lives.
Is cat heartworm contagious?
No, heartworm disease doesn't spread between cats or from cats to other animals.
Heartworms can't jump from one animal to another—they need mosquitoes to move around. The American Heartworm Society explains that cats are unusual hosts; while they can get infected, the worms rarely reproduce inside them. So the only way cats get heartworms is through mosquito bites.
Where do cats get heartworm from?
Cats get heartworm from infected mosquitoes carrying baby worms.
Here's how it works: A mosquito bites an infected animal (usually a dog) and picks up tiny worm larvae. Over 10–14 days, those larvae grow inside the mosquito and become infectious. When the mosquito bites your cat, it leaves the larvae behind, which then travel through your cat's body to the heart and lungs. The CDC strongly suggests keeping mosquitoes under control and using preventive meds year-round.
How likely is it for a cat to get heartworms?
Cats are 5% to 15% as likely as dogs to get heartworms in areas where the disease is common.
In places where heartworms are everywhere, the American Heartworm Society estimates that 5% to 15% of cats may test positive for heartworm antibodies—meaning they've been exposed—compared to dogs, which get infected at much higher rates. Even at those lower odds, heartworms can still kill cats. PetMD puts it bluntly: no cat is safe without prevention.
Can cats be cured of heartworm?
There's no safe cure for heartworm in cats; prevention is the only real option.
Unlike dogs, cats can't handle the arsenic-based drugs used to kill adult heartworms in dogs. Even if your cat seems fine, heartworm infection can cause sudden death from breathing problems or blocked arteries. The Cornell Feline Health Center pushes hard for preventive meds—because once your cat is infected, there's no going back.
Do cats need heartworm protection?
Yes, every cat—no matter how they live—needs year-round heartworm prevention to avoid deadly infection.
Preventive meds come as topical treatments, pills, or injections, and they stop heartworm larvae from growing into adults. The ASPCA suggests starting kittens on prevention as early as 8 weeks old and keeping it up every month for life. Indoor cats aren't off the hook—mosquitoes can still find their way inside.
Do cats really need heartworm prevention?
Yes, heartworm prevention is non-negotiable for cats because the disease is usually fatal and has no reliable treatment.
Preventive meds are cheap, easy to give, and way safer than trying to treat an active infection. The American Kennel Club warns that even one missed dose can leave your cat exposed. Since symptoms often don't show up until the disease is far along, prevention is your only real defense.
What do heartworms look like in poop?
Adult heartworms look like thin, spaghetti-like strands—usually 4 to 12 inches long—and you rarely see them in cat poop or vomit.
That's because cats aren't natural hosts, so adult worms rarely grow or survive long enough to come out. In dogs, though, you might spot these worms in vomit or stool. If you ever see something like that, call the vet immediately. The American Heartworm Society says this is a rare but serious sign in dogs—not something you'd typically see in cats.
Edited and fact-checked by the FixAnswer editorial team.
