Dogs in the USA should receive heartworm preventative pills year-round, 12 months a year, to ensure full protection. Although mosquito activity is highest in warmer months (typically June–November), mosquitoes can survive indoors or emerge during winter warm spells, making year-round protection essential to prevent infection.

What months do dogs need heartworm meds?

When is the heartworm medication taken? During the mosquito season once monthly from June 1st to November 1st. The medication works retroactively. For example; the June 1st dose prevents heartworm disease from developing as a result of mosquito bites during the month of May.

Can you skip Heartgard in the winter?

The way heartworm preventative works is based on the life cycle of the heartworms which is pretty long once the dog has been bitten by a mosquito, so stopping in the winter could prevent protection against a bite that happened a while ago. Best to continue year round.

How long can a dog go without heartworm pills?

You can generally go about 15 days past the due date before an infection becomes likely, but you should give a missed monthly dose immediately if it's less than two weeks late; if it's been over two weeks, contact your vet, as you might need a heartworm test in about six months to be sure, because heartworm larvae take months to mature. Missing doses leaves your dog vulnerable because preventatives only last a short time in the body, so consistent monthly (or year-round) dosing is crucial. 

What are the first signs of heartworms in dogs?

The first signs of heartworms in dogs are often subtle, including a mild, persistent cough (sometimes a "goose honk" sound), lethargy or reluctance to exercise, fatigue after activity, decreased appetite, and weight loss, but many dogs show no symptoms in early stages, making regular vet testing crucial. These initial signs develop as worms grow and damage the heart and lungs, leading to more severe issues like heart failure or respiratory distress as the infection progresses.
 

Ask The Vet - Importance of dog heartworm medication

Is Heartgard really necessary?

The American Heartworm Society recommends giving your dog year-round protection. That's because the threat of heartworm disease doesn't stop with dropping temperatures. Many pet owners might assume that they only need to give their dog heartworm disease preventives when it's warm.

What time of year are dogs most likely to get heartworm?

In most parts of the country, exposure risk is greatest during the warm months of summer and early fall.

What dogs are more prone to heartworm?

The infection risk is greatest in dogs that are housed outdoors. Any dog, whether it is an indoor or an outdoor pet, is capable of being infected; all it takes is a bite from a mosquito carrying the infective heartworm larvae. Most infections are diagnosed in medium- to large-sized dogs that are 3–8 years old.

What kills heartworms in dogs naturally at home?

Anecdotal evidence suggests that herbs such as garlic, black walnut and wormwood, and the homeopathic heartworm nosode, may actually prevent as well as treat infection. Unfortunately, I have not yet been able to find substantive proof that these therapies can reliably and safely prevent or treat infection or disease.

What is the dog disease in 2025?

What are the causes of the dog virus outbreak in 2025? The 2025 dog flu outbreak is caused by highly contagious H3N8 and H3N2 influenza strains, spreading quickly in kennels, parks, and grooming facilities.

Can dogs survive without heartworm medicine?

Not all dogs with heartworm disease develop caval syndrome. However, if left untreated, heartworm disease will progress and damage the dog's heart, lungs, liver, and kidneys, eventually causing death.

Do I need to give my dog NexGard every month?

NexGard chews provide monthly protection that is designed to be administered every 30 days for year-round protection. Keep up with monthly dosage using our monthly reminder tool, so you can ensure your pet is protected all year.

What is the controversy with Heartgard?

The Heartgard controversy centers on allegations that its maker, Merial, falsely advertised the drug as 100% effective, despite internal knowledge and FDA warnings (circa 2009) that its efficacy was closer to 95%, especially as heartworm resistance emerged; lawsuits claimed this deception led to dogs contracting heartworms, causing severe illness, while a whistleblower suit alleged cover-ups and improper data handling by Merial, though the company maintained product safety.
 

What states are worst for heartworms?

North America can carry heartworms. WHERE THE WORMS ARE WORST. The TOP 5 states are: Mississippi, Louisiana, South Carolina, Arkansas, and Alabama.

Can you skip heartworm in winter?

Although there are fewer mosquitoes in the winter, there is still a risk that your pet could get heartworms if you stop giving heartworm prevention medication during this season. That's one reason veterinarians strongly recommend pets receive heartworm prevention medication year-round.

What is the safest heartworm prevention for dogs?

The safest heartworm prevention for dogs involves FDA-approved medications like Heartgard Plus, Interceptor Plus, and Revolution, with the best choice depending on your dog's specific needs, age, and health; Heartgard (ivermectin) is often cited as very safe, even for sensitive breeds like Collies at recommended doses, while Interceptor (milbemycin) is also a good, safer alternative, and Revolution (selamectin) is another gentle option, but always consult your vet to avoid issues with specific sensitivities (like ivermectin in some collies) and to ensure year-round protection. 

Are heartworms visible in dog poop?

Myth #3: If my pet has heartworms, I will see them in her feces. Although many worm types, such as roundworms and tiny hookworms, are shed in your pet's feces, heartworms do not live in the gastrointestinal (GI) tract, and are not found in feces.

What if I forgot to give my dog a heartworm pill for a month?

If you realize you've missed your pet's heartworm medicine by a few days, give the missed dose as soon as you remember, then return to your regular schedule. However, if it's been longer (especially more than a month), don't just resume as normal. The safest move is to call Bixby Animal Clinic for tailored guidance.

What can I give my dog instead of Heartgard?

The chicken-flavored chewable monthly preventative, Interceptor Plus, is a popular alternative to the better-known Heartgard anti-heartworm medication. The main ingredient is Milbemycin Oxime which is anthelminthic.

What breed of dog has ivermectin toxicity?

Ivermectin toxicosis has been reported frequently in Collies; however, other breeds may have idiosyncratic reactions to low doses. Patients with severe toxicosis should eventually recover completely if given appropriate intensive care.

How does a dog get heartworm?

Dogs get heartworm through the bite of an infected mosquito that carries microscopic heartworm larvae, which mature inside the mosquito and are then transmitted to the dog, migrating to the heart, lungs, and blood vessels where they develop into adult worms. The cycle starts when a mosquito bites an infected animal (like a dog, coyote, or wolf), picks up the baby worms (microfilariae), and then bites a new host, injecting the infective larvae, making mosquito control essential for prevention.

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