The Best Heartworm Prevention and Treatment for Dogs

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During my new puppy’s first visit to the vet last month, the vet reminded me that little Rudy should start taking heartworm preventatives at just a few months old. I had heard a rumor that heartworms are not a problem in Seattle, where Rudy and I live, so I asked if it was really necessary.

My vet informed me that, even though Seattle does not have the kind of warm climate where heartworm generally thrives, no matter where a dog lives, “all dogs need heartworm preventative.”

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But why, what is heartworm, and how do dogs get it? We explain how dogs contract the parasite and the various treatments available.

What Is Heartworm?

Heartworm is a parasite that can live in the heart and pulmonary artery of dogs and cats. Full-size heartworms resemble very thin spaghetti and can be up to one foot long. They cause direct damage to the heart and arterial tissue by feeding on the tissue. Heartworms can also block the pulmonary artery, causing reduced blood flow to the heart and lungs, which can result in further damage.

Heartworm disease is very dangerous for dogs and can be fatal. Dogs diagnosed with heartworm may be hospitalized and treated with Melarsomine, and injectable drug, and antibiotics to target bacteria that are associated with heartworm infections. As the heartworm infection is treated and the dog recovers, reduced activity and cage rest are required for a few months.

How Do Dogs Get Heartworm?

Heartworm is transmitted between dogs by mosquitoes. If a mosquito bites an infected dog, tiny heartworm larvae can develop inside the mosquito’s body. After 10-14 days, heartworm larvae can be passed along to another dog when the mosquito bites again.

This 10-14 day incubation period inside the mosquito means that your dog can’t get infected by being at the dog park at the same time as a heartworm-positive dog. But being in the same area as other infected dogs can lead to heartworm infection unless veterinarian-prescribed heartworm medications are part of your dog’s health care routine.

Heartworm is more common in areas with warm weather and long summers, such as the Southeastern US. Common wisdom used to say that dogs in Seattle and other temperate climates don’t get heartworm, but this is no longer true. Dogs all over North America are susceptible to heartworm. For info on the prevalence of heartworm infections in the US, check out The American Heartworm Society’s helpful website.

Heartworm Symptoms in Dogs

As veterinarian Ari Aycock-Williams explains, heartworm disease is often asymptomatic, meaning there are no early signs. However, when signs are seen once the disease has advanced, they include the following:

  • Weight loss
  • Difficulty breathing
  • Diminished exercise tolerance/Lethargy
  • Distended abdomen from fluid accumulation
  • Fainting due to the lack of circulating oxygenated blood
  • Coughing

Preventing Heartworm

Thankfully, heartworm is preventable and treatable.

The key to keeping your dog’s heart and lungs healthy is to avoid heartworm infection in the first place. Avoiding mosquito bites is a good start, but not a reliable way to ensure that your dog will avoid exposure to heartworm, as it’s next to impossible to go through summer with zero mosquito bites.

Prescription medications prevent heartworms from growing inside of your dog, even if your dog get bitten by several infectious mosquitoes over the course of the summer. Heartworm preventatives are usually given monthly and your veterinarian will give you advice on whether heartworm preventative should be used year-round or seasonally in your area.

Active Ingredients in Heartworm Preventative Medications

Four medications are used to prevent heartworms: Ivermectin, Milbemycin, Moxidectin Oxime, and Selamenctin. Many medications include additional active ingredients to treat other internal parasites or fleas. Prescription heartworm medications are available through your veterinarian. These are the active ingredients you’ll see when you read the label:

  • Imidacloprid: Treats flea infestations with very fast knockdown action
  • Ivermectin: Prevents heartworms
  • Lufenuron: Controls fleas by inhibiting their growth and development (but not fast knockdown)
  • Milbemycin: Prevents heartworms, treats internal parasites including hookworm
  • Moxidectin (or Moxidectin Oxime): Prevents heartworms, treats topical and intestinal parasites
  • Praziquantel: Prevents tapeworm and other parasitic worms, but does not treat heartworms
  • Pyrantel Pamoate: Prevents roundworm, hookworm, and stomach worm, but does not treat heartworms
  • Selamectin: Prevents or treats heartworms, hookworms, roundworms, fleas, ear mites, and some ticks
  • Spinosad: Treats flea infestations with very fast knockdown action

Heartworm Preventatives Available Online

Heartworm preventatives require a prescription from a veterinarian, but all of the options listed below can be ordered online. Online veterinary pharmacies such as Chewy, where you’ll find all the options below, make it easy to request a prescription from your vet in order to purchase medications.

Heartgard

Heartgard is a heartworm medication for dogs of all ages starting at 6 weeks. If your dog is on a flea preventative and dewormer already, this might be a good choice because it contains only one active medication.

RX Stats:

  • Chewable Tablet
  • Earliest age: 6 weeks
  • Active Ingredient: Ivermectin

Find Heartgard on Chewy

Heartgard Plus

Heartgard Plus (and the medications Tri-Heart Plus and Iverhart Plus listed below) combines heartworm prevention medication with a dewormer, but does not include flea treatment.

RX Stats:

  • Chewable Tablet
  • Earliest age: 6 weeks
  • Active Ingredients: Ivermectin, Pyrantel

Find Heartgard Plus on Chewy

Interceptor

The active ingredient in Interceptor prevents heartworm infections, as well as roundworm and whipworm infections.

RX Stats:

  • Chewable Tablet
  • Earliest age: 4 weeks (and 2 lbs)
  • Active Ingredients: Milbemycin Oxime

Find Interceptor on Chewy

Interceptor Plus

Interceptor Plus combines one roundworm, whipworm, and heartworm prevention medication with a second medication that prevents tapeworm and hookworm.

RX Stats:

  • Chewable Tablet
  • Earliest age: 6 weeks
  • Active Ingredients: Milbemycin Oxime, Praziquantel

Find Interceptor Plus on Chewy

Tri-Heart Plus

Tri-Heart Plus, just like Heartgard Plus and Iverhart Plus, combines heartworm prevention medication with a broad spectrum dewormer, but does not include flea treatment.

RX Stats:

  • Chewable Tablet
  • Earliest Age: 6 weeks
  • Active Ingredients: Ivermectin & Pyrantel

Find Tri Heart Plus on Chewy

Trifexis

Trifexis prevents infections of heartworm, roundworm, and whipworm, and includes an anti-flea medication with fast knockdown time.

RX Stats:

  • Chewable Tablet
  • Earliest age: 8 weeks (and 5 lbs)
  • Active Ingredients: Spinosad, Milbemycin Oxime

Find Trifexis on Chewy

Sentinel

Sentinel prevents infections of heartworm, roundworm and whipworm, and combines a long-lasting anti-flea medication that inhibits the growth cycle of fleas but does not have super-fast knockdown. This is a good choice for maintaining a flea-free environment.

RX Stats:

  • Chewable Tablet
  • Earliest age: 4 weeks (and 2 pounds)
  • Active Ingredients: Milbemycin Oxime, Lufenuron

Find Sentinel on Chewy

Sentinel Spectrum

Sentinel Spectrum includes roundworm, whipworm, and heartworm prevention medication along with treatment to prevent tapeworm, hookworm, and fleas.

RX Stats:

  • Chewable Tablet
  • Earliest age: 6 weeks
  • Active Ingredients: Milbemycin Oxime, Lufenuron, Praziquantel

Find Sentinel Spectrum on Chewy

Revolution

Revolution is a monthly skin spot treatment that targets heartworms, hookworms, roundworms, fleas, ear mites, and some ticks.

RX Stats:

  • Topical Liquid
  • Earliest age: 6 weeks
  • Active Ingredient: Selamectin

Find Revolution on Chewy

Advantage Multi

Advantage Multi is a monthly skin spot treatment that prevents hookworms, roundworms, and whipworms, and includes fast flea knock down. This combination of active ingredients is also used to treat mange in dogs.

RX Stats:

  • Topical Liquid
  • Earliest age: 7 weeks (and 3 lbs)
  • Active Ingredients: Imidacloprid, Moxidectin

Find Advantage Multi on Chewy

Iverhart Plus Multi

Iverhart Plus (as well as Heartgard Plus and Tri-Heart Plus listed above) combines a heartworm prevention medication with a broad spectrum dewormer, but does not include flea treatment.

RX Stats:

  • Chewable Tablet
  • Earliest age: 6 weeks
  • Active Ingredients: Ivermectin, Pyrantel

Find Iverhart Plus Multi on Chewy

Simparica Trio

Simarica Trio combines a heartworm preventative with a second medication that treats roundworm, hookworm, and stomach worm.

RX Stats:

  • Chewable Tablet
  • Earliest age: 8 weeks (and 2.8 lbs)
  • Active Ingredients: Moxidectin, Pyrantel

Find Simparica Trio on Chewy

Further Reading

No matter where you live, it’s important to discuss heartworm prevention for your dog with your vet. Your vet can give you detailed advice about dosage, the many varieties we’ve presented here, and whether heartworm preventative should be used year-round or seasonally in your area.

If you’re looking for more information about heartworm and other parasites common in dogs, check out one of the links below.

  • How Do Dogs Get Heartworm?
  • Puppy Dewormer: Where to Find the Best Options and How it Works
  • 8 Potentially Deadly (and Preventable) Dog Diseases

Original Article