Heartworm Prevention

What Is Heartworm Disease?

Heartworm disease is caused by parasitic worms (Dirofilaria immitis) that can grow up to a foot long. These worms live in the heart, lungs, and nearby blood vessels of infected pets.

Mosquitoes spread the infection. When a mosquito bites an infected animal, it picks up microscopic heartworm larvae. If that mosquito then bites your dog or cat, the larvae enter the bloodstream and develop into adult worms over about six months.

In dogs, adult heartworms can live for 5 to 7 years and reproduce, leading to higher worm burdens. In cats, fewer worms typically mature, but even immature stages can cause significant harm, including heartworm-associated respiratory disease (HARD).

Without treatment, heartworms damage the heart, lungs, and arteries over time, potentially leading to heart failure, lung disease, or death. The encouraging news is that heartworm disease is almost entirely preventable with year-round medication.

Why Year-Round Prevention Is Essential?

Even a single mosquito bite can transmit heartworm larvae. Once inside your pet, these larvae grow into worms that damage the heart, lungs, and arteries, leading to reduced heart function, breathing problems, organ failure, and, often, death if untreated.

Mosquitoes remain active year-round indoors, in warm spots, or in mild climates, so the risk never fully stops for any pet.

Prevention interrupts the cycle early. Annual testing ensures your pet is free of infection, and safe medications tailored to your pet's needs (monthly oral medications, topicals, or injections) keep them protected. These are easy to give and highly effective.

How do pets get heartworms?

Through mosquito bites only. When a mosquito bites an infected animal, it picks up microscopic larvae. When it bites your pet, the larvae enter the bloodstream and develop into adult worms. Pets cannot catch heartworms directly from other animals.

Can indoor pets get heartworms?

Yes. Mosquitoes enter homes through doors, windows, and small gaps. A significant number of cats diagnosed with heartworm disease are indoor-only. All pets benefit from year-round prevention.

What are the symptoms of heartworm disease?

Early stages often show no symptoms. As the disease progresses, dogs may develop a persistent cough, fatigue, decreased appetite, and weight loss. Cats may show coughing, asthma-like attacks, vomiting, or sudden collapse. By the time symptoms appear, significant damage may already have occurred.

How often should my pet take heartworm prevention?

Most preventives are given monthly and should continue year-round. Some injectable options for dogs provide six- or twelve-month protection in a single dose. Missing even one dose can leave your pet vulnerable.

What happens if I miss a dose?

Give the missed dose as soon as possible and resume your regular schedule. If more than six to eight weeks have passed, contact us before continuing. Your pet may need testing first, since giving preventives to an infected pet can cause serious complications.

Why test if my dog is already on prevention?

No preventive is 100% effective. Missed doses, late doses, or a spit-out chewable can create gaps in protection. Annual testing catches infections early before they cause serious harm. Testing is also required before starting or restarting prevention.

Is heartworm disease treatable?

In dogs, yes, but treatment is lengthy, costly, and carries some risk. It involves multiple injections over several months, along with strict exercise restrictions. There is no approved treatment for cats. Infected cats can only be managed with supportive care, making prevention essential.

Is heartworm prevention safe?

Yes. Heartworm preventives have been used safely for decades. Side effects are rare and typically mild. The risk of heartworm disease far outweighs the minimal risks of prevention.

Do cats really need heartworm prevention?

Yes. Cats are less susceptible than dogs, but they can still become infected. Even a small number of worms can cause serious illness or death in cats, and there is no treatment. Prevention is essential for all cats, including those who never go outside.

What's the best heartworm prevention for my pet?

It depends on your pet's species, size, lifestyle, and health. Options include monthly chewables, topicals, combination products that also cover fleas and ticks, and long-lasting injectables for dogs. We'll help you choose the best fit.