Few canine conditions are as frightening as heartworm disease. Difficult and potentially dangerous to treat, heartworms are nothing you want your dog to rumble with.
Luckily, you can prevent this scary parasite by offering your pooch a heartworm preventative.
We’ll explain heartworms, breakdown how heartworm preventatives and treatments work, and identify a few of the best heartworm prevention medications for dogs below.
Best Heartworm Prevention for Dogs: Quick Picks
- #1 Heartgard Plus Soft Chews [Best Overall Heartworm Prevention for Dogs]: A long-trusted favorite by veterinarians, dog owners have howled its praises for years and continue to today.
- #2 Tri-Heart Plus Chewables [Most Affordable Heartworm Prevention for Dogs]: This ivermectin-based preventative keeps your four-footer safe from heartworm disease for less.
- #3 Revolution Topical Solution [Best Topical Heartworm Prevention for Dogs]: Perfect for picky pups, this topical preventative protects your dog against a wide range of parasites.
What Is Dog Heartworm?
Scientifically known as Dirofilaria immitis, heartworms are parasites that infest the heart and lungs of host animals. These creepy crawlies can grow over a foot long and cause severe cardiac and pulmonary damage and blockages, leading to the host animal’s eventual death.
Dogs aren’t the only animals that can get heartworms, as cats and ferrets are also at risk. But sadly, canines are the most commonly infected species, as a dog’s body is the perfect place for these dangerous parasites to hide.
In rare cases, humans can contract heartworms, but they typically don’t make it to maturity, as we’re not the parasite’s natural host.
How Do Dogs Get Heartworms?
Mosquitos act as a conduit between dogs and heartworms, carrying the parasites for a short time while they mature. Eventually, they’ll end up passing the heartworm larvae on to dogs when feeding on four-footers.
Once transmitted, the heartworm larvae (called microfilariae) live in a dog for several months before releasing offspring into the dog’s bloodstream.
The disease will progress from there for the afflicted dog, and he can also serve as an additional vector for the parasite — mosquitos feeding on him from this point forward may pick up and transmit the parasites to other dogs.
Heartworm disease is most common in the southeastern U.S. but the ailment has been reported in all fifty states.
Because of this widespread distribution, all dogs should take a heartworm preventative (pending your vet’s recommendation to do so), regardless of where they live. It’s a cheap, easy form of protection against these deadly parasites.
Heartworm disease is not directly contagious; it requires mosquitos to spread. So, you won’t contract it from a dog, nor will your dog catch it from another pooch at the park.
But puppies born to a heartworm-positive mama can harbor microfilariae in their bodies. Fortunately, these larvae won’t mature without passing through a mosquito. However, the dog is still vulnerable to heartworm disease from a mosquito bite without a heartworm preventative.
Is Heartworm Dangerous for Dogs?
Heartworm disease is incredibly dangerous to dogs. Full stop.
The worms cause heart and lung damage as well as stress your dog’s system as they take up more and more space. This makes it harder for your dog’s body to pump blood through the body and can lead to leaky valves and ultimately heart failure.
Unfortunately, heartworm disease is also a silent threat at first, with a great deal of harm inflicted before your dog begins to show symptoms.
Most infested dogs carry an average of 15 heartworms, but this number (also called worm burden) can reach upwards of 250 worms. You don’t want your dog to have any heartworms, but the greater the number of worms present, the more destruction to the body they cause.
Newly infested and inactive dogs typically have less of a worm burden than very active dogs or those who’ve been infested for a long time.
Over time, heartworm disease can lead to caval syndrome, where the worms cause a blockage that requires immediate surgery and removal of the worms, or the host animal will die.
Sadly, most dogs who reach this stage pass away anyway, sometimes even after surgery.
What Are the Symptoms of Heartworm in Dogs?
As mentioned above, heartworm infestation often has no initial signs, making it incredibly difficult to catch.
The disease is broken down into four severity classes with varying symptoms, with higher class numbers correlating with more serious infestations and worse side effects.
Heartworm disease classes and their respective symptoms include:
- Class 1: Most newly infected dogs fall in this group, and they may show no symptoms or, at most, a slight, occasional cough.
- Class 2: Dogs in this class may exhibit occasional coughing and lethargy — especially after exercise.
- Class 3: A frequent cough is seen in dogs in this class, along with a change in appearance, such as a bloated belly or sickly look. Such dogs avoid exercise or only do so with great difficulty. Breathing trouble and a lack of appetite are also common, leading to weight loss.
- Class 4: Also known as caval syndrome, patients in this class have notable difficulty breathing and weakness. They may faint or collapse, and blood may be present in their urine. Their gums are usually pale, and they have irregular heartbeats. At this stage, death is expected within 72 hours without treatment.
How Do I Know If My Dog Has Heartworm?
As mentioned, heartworm disease doesn’t always cause obvious symptoms — especially at the outset.
Fortunately, heartworm disease can be detected through blood testing.
These tests look for the proteins released by female heartworms called antigens. They can also look for the presence of microfilariae in your dog’s blood.
Unfortunately, neither of these appear until months after your dog has been bitten by an infected mosquito.
This makes routine testing essential when your pup has his annual exam and before starting a preventative regimen.
Testing before starting a heartworm preventive is critical, as preventatives do not kill adult heartworms.
Giving a heartworm-positive dog a preventative will also kill any microfilariae in your dog’s blood, potentially triggering a dangerous shock-like reaction that can be deadly.
Your dog may also need a heartworm test in some other circumstances.
For example, if you miss a dosage of preventative, are switching preventatives, or if your dog has recently traveled with you to a place where heartworm disease is more common, your vet will likely recommend a blood test.
Can Heartworm Be Treated or Prevented?
Heartworm disease can be treated, but it’s a long, expensive road to recovery, and you’ll have to start by addressing any adult worms present.
In heartworm-positive dogs falling between classes 1 and 3, parasite-killing injections can be given once the dog’s condition is stabilized.
The injections kill adult heartworms and are only administered in a veterinary setting, as your pooch will require hospitalization and close monitoring. This is necessary because some patients experience inflammation or respiratory distress after receiving these medications.
Once the adult worms have been handled, you can begin treating the larval worms in your dog’s body. This part is generally a little safer than the eradication of the adults, but it still poses serious risks.
Existing microfilariae in the bloodstream are eliminated with heartworm preventatives. But you can’t just administer the medications and go back to normal life.
Instead, you’ll need to keep your dog crated with limited activity and excitement for four to six weeks during treatment, with frequent vet appointments needed for examinations and blood tests to monitor your dog’s condition.
This reduced activity is critical, as dying worms in your dog’s bloodstream can be propelled into smaller veins and capillaries with too much exercise, leading to a life-threatening pulmonary embolism.
For canines with advanced heartworm disease (class 4), surgery is required to remove all adult worms. This surgery is incredibly dangerous, with some dogs passing during or after the procedure, despite the removal of all worms.
Your dog will be retested in six months, and if the heartworms are still present, the treatment process has to start over, beginning again with the injection. If no heartworms are detected, your dog is cleared to go on with a year-round heartworm preventative and hopefully live a long, happy, parasite-free life.
Prevention is always better than treatment with heartworms, as treatment is risky and expensive, lasting months and greatly impacting your dog’s day-to-day life. Through regular checkups and a strict administration of heartworm preventative, you can keep your pupper safe from this harmful parasite.
Dog Heartworm Prevention Medications: Active Ingredients
Heartworm preventatives come in many shapes in sizes, from injections to topicals to tasty chews, though they all have the same goal: to prevent your dog from contracting heartworms.
That said, these medications have different active ingredients, with some banishing just heartworms while others prevent additional worms and parasites too.
The most common active ingredients in heartworm preventatives include:
- Ivermectin: Used in Heartgard Plus, Iverhart, and more, this prevents heartworm infestation.
- Selamectin: Found in Revolution, it prevents a host of parasites, including heartworms, hookworms, roundworms, mites, fleas, and some species of ticks.
- Milbemycin oxime: Used to prevent heartworms and treat hookworm infestations, it can be found in Trifexis, Sentinel, and more.
- Moxidectin: Included in Proheart and Advantage Multi, it kills heartworm larvae and treats some intestinal parasites.
- Imidacloprid: Found in Advantage, it’s an insecticide that’s used to treat flea infestations and can help with heartworm treatment.
- Lufenuron: Featured in Sentinel and Spectrum, it’s used to prevent flea infestations by preventing them from growing and can help in heartworm treatment.
The 7 Best Heartworm Prevention Medicines for Dogs
Because they can be dangerous if not used properly (such as when they’re administered to a dog who already has heartworm disease), Heartworm preventatives require a prescription from your vet — whether you buy them from Chewy or some other online pet pharmacy.
But once you have a prescription in hand and your vet’s recommendation regarding a specific drug, you’ll be in business.
Some of the best heartworm prevention medicines include:
1. Heartgard Plus Soft Chews
Heartgard Plus Soft Chews
A time-tested, tasty, and easy-to-administer medicine to help prevent heartworm in dogs.
About: Heartgard Plus Soft Chews are a time-tested heartworm preventative that remains well-loved by dogs, vets, and owners alike. As the number-one prescribed heartworm preventative, over two billion doses and counting have been administered.
- Made in a delicious beefy bite-sized nugget
- Treats hookworm and roundworm infestations too
- Requires a monthly dose
- Made in the USA
Available in three dosages for dogs weighing up to 100 pounds.
Ivermectin and Pyrantel
- This medication is easy to administer, thanks to its beefy flavor.
- Owners rave about the efficacy of this drug.
- Despite being very effective, this heartworm prevention medication isn’t especially expensive.
- Some dogs had minor digestive upset after eating this medication, but this is an acceptable tradeoff for protection from heartworm disease.
- Certain breeds can’t safely consume ivermectin, like collies and some other herding dogs.
2. Tri-Heart Plus Chewables
Tri-Heart Plus Chewables
A tasty and budget-friendly heartworm prevention medication for dogs.
About: Prevent heartworm and control other parasites with Tri-Heart Plus Chewables. With a six-month supply costing as much as a bag of kibble, it’s hard to beat the price of this preventative.
- Ivermectin-based formula prevents heartworm infestation with a monthly dose
- Comes in a tasty chewable
- Helps treat hookworm and roundworms
- Made in the USA
Available in three dose options: 1 to 25 pounds, 26 to 50 pounds, and 51 to 100 pounds.
Ivermectin and Pyrantel
- This product is incredibly affordable, with a six-month supply costing less than $40.
- Dosing your dog with a chewable is generally easier and creates less of a mess than topical solutions.
- These chewables are easy to crush and hide in food if you have a picky pup.
- Some breeds (collies and other herding breeds) cannot safely consume ivermectin.
- The taste of these chews wasn’t a hit with every dog.
3. Revolution Topical Solution
Revolution Topical Solution
A topical alternative to chewable tablets for protecting your dog from heartworm disease.
About: Revolution’s Topical Solution protects your dog from heartworm disease with a monthly application. Safe for use in dogs and puppies 6 weeks old and above, just apply to your pup and banish parasites for good.
- Must be applied monthly to your dog’s skin for full protection
- Quick-drying, greaseless formula goes on fast and mess-free
- Protects against fleas, ticks, and ear mites too
- Made in the USA
Available in six solution strengths for dogs ranging from less than 5 pounds to 130 pounds.
- Covering dogs up to 130 pounds, this is a good choice for large and giant breed owners who may have a hard time finding another topical that works.
- With nothing to ingest, you don’t have to worry about picky pups or this medicine causing or upset tummies.
- Dogs with ivermectin sensitivities tend to tolerate Revolution.
- Safer for use around cats than other preventative topicals.
- Some owners found the scent of this heartworm prevention medication to be off-putting.
- Some owners found this product to be less than impressive against fleas and ticks.
4. Inceptor Chewable Tablets
Inceptor Chewable Tablets
Effective heartworm prevention chewables that also eliminates other internal worms.
About: Inceptor Soft Chews defend your dog against a host of parasites, including not only heartworms, but hookworms, and some other worms too. An ivermectin-free formula, this medication is a popular alternative for four-footers who can’t have ivermectin and dogs with sensitive systems.
- Provides protection against heartworm with one yummy monthly chewable tablet
- Safe for use in dogs and puppies 4 weeks old and above
- Helps treat and eliminate whipworm, roundworm, and hookworm infestations
- Made in the USA
Available in four size coverages, ranging from 2 to 100 pounds.
- This product provides comprehensive parasite protection for puppies as young as 4 weeks (2 weeks sooner than most brands!)
- This product’s taste gets a wag of approval from most dogs.
- A weight limit starting at 2 pounds makes this medication ideal for toy breeds that might be too small for other brands.
- Some dogs dislike the texture of this product, though it can be easily crushed and hidden in food for administration.
- A few owners reported their pups had an upset tummy after eating these chews.
5. Trifexis Chewable Tablet
Trifexis Chewable Tablet
A heartworm prevention medication that also kills other types of pooch-plaguing parasites.
About: Trifexis Chewable Tablets battle heartworms, fleas, hookworms, roundworms, and more in one delicious pill. An excellent pick for pups with flea allergies, it starts killing fleas within a half hour of ingestion.
- Is the top-prescribed parasite prevention combo
- Safe for use in dogs and puppies 8 weeks old and above.
- Features an enticing beef flavor
- Made in the USA
Available in five strengths, covering dogs from 5 pounds to 120 pounds.
Spinosad and Milbemycin Oxime
- With no ivermectin, this is a good heartworm prevention option for dogs with sensitivities.
- It’s also an excellent choice for owners looking for comprehensive parasite coverage.
- This product is very reasonably priced, considering you’re getting heartworm and flea preventative in one chewable.
- Some dogs experience stomach upset after eating these tablets.
- With the weight limit starting at 5 pounds, this medication isn’t safe for some toy breeds.
6. Sentinel Flavor Tabs
Sentinel Flavor Tabs
A tasty heartworm prevention medication that’s ideal for finicky four-footers.
About: Sentinel Flavor Tabs are a picky pup’s dream with their delicious beef taste. Smaller than other heartworm preventatives, they’re also easy to hide in other goodies if your dog is ultra persnickety.
- Protects your dog against heartworms, roundworms, hookworms, and whipworms
- Safe for use in dogs and puppies aged 4 weeks and older
- Disrupts the life cycle of fleas, preventing eggs from hatching
- Made in Italy
Comes in four strengths, covering dogs weighing 2 to 100 pounds.
Milbemycin Oxime and Lufenuron
- The flavor of this product is a clear winner compared to other preventatives.
- With a weight limit starting at 2 pounds, this medication is an excellent choice for toy breeds who may be too tiny for other preventatives.
- The lack of ivermectin makes this medicine a good fit for collies and other herdings breeds that can’t ingest ivermectin.
- This product is a bit expensive compared to other chewables.
- Some pup patients experienced mild stomach upset after eating these heartworm prevention tabs.
7. Advantage Multi Topical Solution
Advantage Multi Topical Solution
A budget-friendly topical medication to protect your dog from heartworm disease.
About: For pup parents seeking a heartworm preventative that doesn’t require ingestion, check out Advantage Multi Topical. There’s no need to fuss with hiding any pills, just squeeze the tube on your dog’s skin in the designated location, and you’re good to go.
- Apply once a month to your dog’s skin to prevent heartworms
- Treats hookworms, roundworms, and whipworms
- Kills and repels fleas and mange
- Made in Germany
Sold in five size options, ranging from 3 to 110 pounds.
Imidacloprid and Moxidectin
- This medication provides one-stop protection against some of the most common parasites, which saves you time and money.
- Many owners found this product to be easy to apply and grease-free, unlike many other topicals.
- This is an excellent choice for dogs with sensitive tummies or picky palates who may struggle with oral preventatives.
- Topicals can be dangerous in multi-species households where cats are present.
- Some owners disliked the smell of this medicine.
Heartworm Disease in Dogs: FAQs
Don’t feel bad if you still have questions about heartworm disease in dogs! There’s a lot to learn and the stakes are pretty high, so it’s important to make sure you know everything you need to.
We’ll try to answer a few of the most common questions below to fill you in!
What Happens If My Dog Already Has Heartworms?
If your dog already has heartworms, you’ll need to work with your vet to outline a treatment plan. This includes stabilizing your dog and determining how severe the heartworm disease is.
From there, your vet will begin treatment, which may consist of injections, hospitalization, surgery, and more.
Is a Heartworm Preventative Needed Year-Round?
Even if you live somewhere that mosquitoes are only present seasonally, year-round heartworm prevention is recommended. This keeps your dog protected in case of travel or stowaway insects in indoor environments.
Year-round prevention protocols also provide seamless protection against microfilariae that may lie dormant in your pup’s system.
What If I Miss a Dose of Heartworm Preventative?
Heartworm prevention medication has to be given according to a strict, unbroken schedule for total protection. If you miss a dose, you’ll want to contact your veterinarian and consult the product literature to see whether or not it is safe to administer.
Depending on the time between doses, your vet may recommend heartworm testing in six months.
Are There Any Risks With Heartworm Preventatives?
Every medication comes with risks, including heartworm preventatives. Some breeds, such as members of the collie family, are sensitive to certain active ingredients in medications, so it’s always best to consult with your vet.
Since a prescription is needed for heartworm prevention medicines, your vet will likely discuss these with you and help you make the best choice for your fur kiddo. He or she will also highlight any side effects you should watch for, like lethargy or digestive upset.
Heartworm disease is a formidable foe, but thankfully, sticking to a preventative routine can block infestation and keeps your doggo feeling his best.
Do you use any of the heartworm preventatives on our list? Do you use another we didn’t mention? Let us know in the comments.