The Best Heartworm Prevention for Dogs (7 Medication Reviews)

What is Heartworm Prevention for Dogs?

The best heartworm prevention for dogs is advisable for all dogs. Heartworm medication works by treating heartworms that have already affected the pet in the previous month or longer; nevertheless, to be effective, you must give preventives every time. The American Heartworm Society promotes heartworm prevention for pets all year.

two vets with dog

Our Top Pick for the Best Heartworm Prevention for Dogs

Our best heartworm prevention for dogs is Advantage II 6-Dose Large Dog Flea Prevention. It is efficient for killing fleas at all stages of their life cycle, including eggs, larvae, and adults, thus breaking the flea life cycle and preventing flea infestation on your dog. 

The Dangers of Heartworm Disease in Canines

Heartworms in Dogs can cause serious health problems. There are no obvious or measurable indicators of heartworm infection in a dog when first affected. A blood test will first fail to detect heartworms.

The alterations in dogs occur during the heartworm larval’s final molt when young larvae enter the right ventricle and surrounding blood arteries. When you notice indicators of heartworms in your dog, it’s because of two things:

  • The worms’ effects on the arteries in the lungs (pulmonary arteries)
  • The amount of blood flow restriction caused by inflammation, as well as the quantity of heartworms present

Another issue that some animals suffer is an allergy to heartworms or microfilariae, which can produce various symptoms comparable to allergies or asthma.

Damage to the Arteries

The arterial lining of your pet will begin to deteriorate within days. To cure the damage, the body causes inflammation of the artery and additional inflammation in the surrounding area.

Unfortunately, heartworms cause harm faster than the body’s ability to repair. The arteries develop characteristics that are diagnostic of heartworm illness over time, and these changes are often visible on X-rays. The vessels dilate and become convoluted. Blood clots and aneurysms are common adverse effects, and small blood vessels might block completely.

Fluid Accumulation and Blood Flow Blockages

The presence of heartworms in your dog’s body can obstruct regular blood flow significantly. Depending on your dog’s blood vessel size, even one worm might severely damage it.

Blood will redirect to worm-free arteries, resulting in full and partial blood vessel obstructions. Fluid builds up around these blood arteries in the lungs, reducing the lung’s ability to oxygenate the blood.

Use an example of a garden hose. When debris obstructs water flow via the hose, pressure builds up. When more and more heartworms collect within the right ventricle, this is what happens to the heart and blood arteries.

The heartworm cough will appear due to inflammation, blood vessel obstruction, and fluid accumulation. Exercise intolerance, shortness of breath, nosebleeds, and weight loss may also be present in your pet.

Heart Failure

Your dog’s reactions will become more noticeable as small worms continue to arrive and mature in the heart and lungs, and the indications will increase. Damage to the blood arteries and lung tissue causes blood pressure (hypertension) in the right side of the heart and the vena cava, finally leading to heart failure.

The quantity of worms present and the dog’s sensitivity to the worms determines the severity of heartworm infection.

The Causes of Canine Heartworms

A single bite from mosquito-carrying heartworm larvae is all it takes to infect your dog. This mosquito may have blood from a dog or a wild animal containing heartworm larvae. After migrating through the circulatory system and settling in the pulmonary veins and the heart, the larvae carried by the mosquito develop into an adult worm in your dog.

You should test all canines above seven months for heartworm every 12 months for the rest of their lives. If they test positive, you will start the treatment early enough. You require only one drop of blood for the test, and your veterinarian will have the findings in less than 10 minutes.

How to Confirm the Diagnosis of Heartworms

To find out the impact of the heartworm infection on your dog’s health, the veterinarian will usually prescribe X-rays, a complete blood count (CBC), a chemical profile (evaluates the function of the body’s organs), and a urinalysis.

Heartworm-positive dogs who show signs of heart illness may get a complete cardiac examination and an analysis of any other body area suggested by the initial test findings.

The veterinarian will analyze the severity of the infection after examining your dog to identify which of the four heartworm classes your dog belongs to. Your veterinarian can determine the best treatment method for you by assessing the type of heartworm illness you have. The severity of the disease has five different classifications:

Lowest Risk 

These dogs are young and healthy, with only a small amount of heartworm illness visible on X-rays, but all other tests are negative.

Moderately Affected

Coughing and trouble breathing are common in Class II dogs. X-rays reveal changes, and blood tests may indicate kidney and liver disease.

Severely Affected

Coughing, trouble breathing, and considerable weight loss are all symptoms that dogs encounter. X-rays show apparent damage, while blood tests reveal kidney and liver damage.

Caval Syndrome 

The dog is in shock and collapses. All of the preceding abnormalities are intense, and the dog is on the verge of death. When a dog reaches Class IV, surgical removal of some worms is advisable. However, there is no guarantee that this treatment will work. Many patients with Caval syndrome succumb to the disease during or after treatment.

The Symptoms of Heartworms in Dogs

Heartworm infection can often go undetected at first, making it extremely difficult to treat.

The following are the heartworm illness symptoms:

  • Most newly infected dogs fall into this category and may show no signs or a minor, intermittent cough.
  • The dog is prone to coughing and lethargy, especially after exercise.
  • Dogs may have a recurrent cough and a change in appearance, such as a swollen tummy or a sickly aspect. Such dogs either avoid exercise or do it only reluctantly. Weight loss is also prevalent due to breathing problems and a lack of appetite.
  • Patients in the last stage of illness have difficulty breathing and are feeble. They could pass out or collapse, and you can find blood in their pee. Their gums are usually pale, and their heartbeats are erratic. Without treatment, death is likely within 72 hours at this point.

Can Heartworms be Prevented?

Heartworm prevention is always preferable to heartworm treatment, which is risky and expensive, lasts for months, and significantly influences your dog’s daily life. You may protect your dog from heartworm by having frequent exams and strictly administering heartworm prevention.

Heartworm medications for dogs come in various forms and sizes, ranging from injections to topicals to delectable chews, but they all have the same goal: to keep your dog safe from heartworms.

However, the active components in these heartworm meds vary, with some preventing only heartworms and others preventing other worms and parasites.

The following are the most prevalent active components in dog heartworm preventatives:

  • Ivermectin: This inhibits heartworm infestation and is present in products like Heartgard Plus, Iverhart, and others.
  • Selamectin: Prevents heartworms, hookworms, roundworms, mites, fleas, and several tick species. 
  • Milbemycin oxime is a component in Trifexis, Sentinel, and other products to prevent heartworms and cure hookworm infections.
  • Moxidectin is a heartworm larvae killer that is also useful in treating some intestinal parasites. 
  • Lufenuron: You can Find it in Sentinel and Spectrum; this insecticide reduces flea infestations by inhibiting their growth and can also aid in heartworm therapy.

Heartworm disease is treatable, but it’s a long and expensive process, and you’ll need to start by eliminating any adult worms. You can’t give your dog a dewormer for dogs and call it a day like you can with other worms.

You can kill adult heartworms by injections, which you only get in a veterinary facility because your dog will need hospitalization and close monitoring. Because some patients have inflammation or respiratory discomfort after taking these drugs, this is important.

After dealing with the adult worms, you can start treating the larval worms in your dog’s body. This stage is often safer than the adult elimination but carries considerable dangers.

Heartworm prevention for dogs destroys existing microfilariae in the circulation. However, you cannot simply administer the drugs and return to your daily routine.

Instead, during therapy, you’ll need to keep your dog crated with minimal activity and excitement for four to six weeks. You will also require frequent vet visits for inspections and blood tests to check your dog’s condition.

Too much exercise can force dying worms in your dog’s bloodstream into smaller veins and capillaries, resulting in a life-threatening pulmonary embolism.

Surgery is essential to remove all mature worms in dogs with severe heartworm disease. This surgery is extremely risky despite removing all worms, and some dogs die during or after the procedure.

In six months, repeat the tests for your dog, and if the heartworms are still present, the treatment process will have to start over, starting with the injection. If no heartworms are present, your dog is safe to continue taking year-round worm prevention for dogs and live a long, happy, parasite-free life.

Dog and pills

The Best Dog Heart Wormers at a Glance

  1. Advantage II 6-Dose Large Dog Flea Prevention: Best overall
  2. FRONTLINE Plus Flea and Tick Treatment for Dogs: Best for senior dogs 
  3. DURVET 12-Pack Triple Wormer Tablets for Puppies and Small Dogs: Best oral med
  4. K9 Advantix II Tick and Flea Prevention for Medium Dogs: Best for all breeds
  5. K9 Advantix II Tick and Flea Prevention for Small Dogs: Best for application
  6. Triple Medium and Large Dog Wormer: Best for different worms
  7. PetArmor 7 Way De-Wormer for Dogs: Best for medium dogs

What to Look for in Heartworm Medicine for Dogs

Do you still wonder which dog heartworm medication is best for your dog? Considering the crucial characteristics outlined below, we’ll assist you in narrowing down your preferred decision.

Active Ingredients

Several typical active compounds are present in heartworm medicine for dogs. Understanding these active components is crucial because dogs can have allergies and other reactions to them. Some of these ingredients may have potentially harmful side effects.

When looking for heartworm therapy for dogs, you’ll probably certainly come across the following substances:


One of the most popular active ingredients in heartworm treatment is ivermectin. You can also use it to treat parasites and mites in the intestine.

When you give your pets the right amounts, this substance seldom causes unwanted effects. An unsettled stomach is the most typical side effect.

It’s important to know that ivermectin sensitivity can occur in herding breeds like Collies owing to a genetic mutation. This mutation is not active in all herding breeds because it is unique to each dog.

Milbemycin Oxime

This is another common preventative treatment for heartworm and other internal parasites. It’s also sometimes useful with flea medicine to make a broad-spectrum dog treatment.

This chemical is commonly given orally to dogs; you can provide it with or without food. Give your dog some food to eat if it has an upset stomach.

Milbemycin oxime interacts with cyclosporine, amiodarone, diltiazem, azole antifungals, and erythromycin, among other medicines. It may also affect some vitamins and supplements. 


The majority of heartworm drugs aren’t just for heartworms. Various dewormers for other internal parasites are included. Ivermectin has a combination of pyrantel, which is a common active component. It’s a dewormer you can use to treat roundworms, hookworms, and other types of stomach worms.

Some less common side effects include vomiting, nausea, loss of appetite, and diarrhea. Taking this medication with meals is advisable because taking it on an empty stomach can cause vomiting. Vomiting, diarrhea, and a loss of appetite are common side effects of parasite removal.

Pyrantel is generally safe for pregnant and nursing animals; however, you must administer the correct dosage. It’s also conceivable that it causes allergies in some pets. Among other drugs, it interacts with levamisole, morantel, piperazine, and organophosphates.


Heartworms, ear mites, fleas, scabies, and some ticks are treated with selamectin and antiparasitic. You apply topically to healthy skin. Because it’s so hot right now, dogs mustn’t receive a bath for at least two hours after coming into touch with it.

For the most part, this substance is safe for pregnant dogs. Herding breeds, like ivermectin, can be particularly sensitive to it. Selamectin may interact with the following medications:

  • Amiodarone
  • Carvedilol
  • Clarithromycin \ Cyclosporine
  • Diltiazem
  • Erythromycin
  • Itraconazole
  • Ketoconazole
  • Quinidine
  • Spironolactone
  • Tamoxifen
  • Verapamil


You can take Moxidectin orally or apply it topically. You can use an antiparasitic to treat intestinal worms and heartworms. To treat fleas, use it with imidacloprid. If your dog receives topical medication, wait at least five days before bathing it.

There aren’t many negative side effects. On the other hand, Moxidectin can produce fatal symptoms in dogs sensitive to milbemycin. As a result, consulting a veterinarian before using Moxidectin is essential.

Moxidectin has no reports of interfering with any drugs. However, if your dog is on a benzodiazepine treatment, give it with caution.

What is the Best Heartworm Prevention for Dogs – Our Reviews

Advantage II 6-Dose Large Dog Flea Prevention: Best Overall

Amazon’s Choice in Dog Flea Drops by Advantage

Brand: Advantage

Item Weight: 0.1 pounds (0.04 kilograms)

Active Ingredients: Imidacloprid

Breed recommendation: Dogs

Size recommendation: Large dogs

Lifestage: All life stages

Administration Form: Lotion

Instructions for use: Use on dogs and puppies above 7 Weeks

About This item

  • Advantage II topical flea and lice treatment for large dogs weighing 21 to 55 pounds (9.53 to 24.97 kilograms) is a veterinarian-recommended monthly application that kills fleas by contact, meaning they don’t have to bite your dog to die. Humans and other pets can transmit fleas into your home, so even indoor dogs need flea protection. 
  • Advantage II’s protection kills fleas at all stages of their life cycle, including eggs, larvae, and adults, thus breaking the flea life cycle and preventing flea infestation on your dog. This 6-dose dog flea treatment comes in an easy-to-apply topical lotion that is fragrance-free and waterproof after 24 hours. 
  • Advantage II flea medication for dogs starts working in 12 hours and kills fleas for 30 days after a single application. Advantage II flea control comes in packs of four or six monthly applications for dogs of all sizes. 
  • Advantage II also comes in a cat-friendly formula. With the help of Advantage II 6-dose flea and lice treatment for large dogs, you may put an end to the anguish of biting fleas.
  • It contains Flea treatment and prevention tubes that are easy to use, pre-measured, fragrance-free, and created exclusively for dogs.
  • Fleas die by touching Advantage II big dog flea medication, so they don’t have to bite your dog to die.
  • It’s a Flea and lice treatment for dogs that is vet-recommended, fragrance-free, and specifically for treating and preventing fleas and lice.
  • Possible side effects: skin reaction.


  • It starts functioning within 12 hours of application, making it a fast-acting treatment.
  • It is an odorless substance.
  • Flea treatments destroy fleas at all phases of their life cycle, protecting pets from disease.


  • Side effects are possible.

Possible Side Effects

  • May cause a skin reaction.

FRONTLINE Plus Tick and Flea Treatment for Dogs: Best For Senior Dogs

Amazon’s Choice in Dog Flea Drops by Frontline

Brand: Frontline

Item Weight 1.6 ounces (45.36 grams)

Active Ingredients: Fipronil and (S)-methoprene 

Breed recommendation: Dog

Size recommendation: Senior

Lifestage: All life stages

Administration Form: Drops

Instructions for use: Avoid contact with skin

About This Item

  • For more than 20 years, veterinarians recommend FRONTLINE Plus for Dogs for flea and tick prevention in dogs. This fast-acting, long-lasting flea and tick control for dogs and puppies eight weeks and older, 45 to 88 pounds (20.43 to 39.95 kilograms), has two harsh killing chemicals, fipronil and (S)-methoprene – one to kill adult fleas and ticks and the other to kill flea eggs and larvae.
  •  Its long-lasting composition stays in the oil glands of the pet’s skin for a full 30 days of flea and tick prevention.
  • This waterproof, fast-acting flea and tick treatment kill fleas, flea eggs, lice, and ticks, including those that may transmit Lyme disease.
  • This long-lasting treatment is only for dogs and puppies eight weeks or older. 
  • This therapy, which contains two active components, fipronil and (S)-methoprene, kills existing infestations while preventing new ones.
  • The therapy quickly covers your dog’s entire body and accumulates in the sebaceous glands after application to a single location on its body. These glands act as a reservoir, regularly refilling the treatment on your pet and continuing to perform even if your dog gets wet.


  • This product is effective at all stages of the flea life cycle.
  • Kills most common pests. 
  • There is no need to measure anything.
  • Works fast and effectively.
  • The formulation is both waterproof and long-lasting.


  • It is expensive

Possible Side Effects 

  • Skin reaction.

DURVET 12-Pack Triple Wormer Tablets for Puppies and Small Dogs: Best Oral Med

Amazon’s Choice in Dog Wormers by Durvet

Brand: ‎Durvet

Item Weight: 0.63 Ounces (17.86 grams)

Active Ingredients Pyrantel pamoate and praziquantel

Breed recommendation: Dogs

Size recommendation: Dogs and puppies

Lifestage: All stages

Administration Form: Tablet

Instructions for use: Use the instructions on the package.

About This Item

  • Triple Wormer in dogs and pups controls Roundworms (Toxocara Canis, Toxascaris leonina), hookworms (Ancylostoma caninum, Ancylostoma braziliense, Uncinaria stenocephala), and tapeworms (Dipylidium caninum, Taenia pisiformis). 
  • It is a convenient pack of 12.
  • Controls seven types of tapeworms, including hook and roundworms, without requiring a prescription.
  • Simple and practical chewable medication.


  • It contains Praziquantel, a worm infection treatment.
  • It’s easy for pets to ingest because it’s in a chewable form.
  • It contains pyrantel pamoate, which kills seven different kinds of worms.


  • Dogs may get drowsy as a result of the medication.

Possible Side Effect 

  • Drowsiness.

K9 Advantix II Tick and Flea Prevention for Medium Dogs: Best For All Breeds

Brand: K9 Advantix

Item Weight: 1.6 ounces (45.36 grams)

Breed recommendation: Dogs

Size recommendation: All breeds

Lifestage: All stages

Administration Form: Drops

Active ingredients: Imidacloprid 8.80%, permethrin* 44.00%, pyriproxyfen 0.44%, other Ingredients 46.76%

Instructions for use: Use only on dogs

About This Item

  • K9 Advantix II is for use on all breeds of dogs weighing more than 4 pounds (1.81 kilograms) at least seven weeks old. Determine which size is appropriate for your dog based on their weight. Choose the size that accommodates your dog’s current weight if your dog is on the cusp. 
  • Consider buying a smaller pack count if you have a growing puppy who will likely exceed the product’s weight limitations within a few months. Notably, small dogs weigh 4 to 10 pounds (1.81 to 4.54 kilograms), medium dogs weigh 11 to 20 pounds (4.99 to 9.08 kilograms), large dogs weigh 21 to 55 pounds ( 9.53 to 24.97 kilograms), and extra-large dogs weigh more than 55 pounds (24.97 kilograms).
  • Apply the full contents of the tube in even locations along the top of the dog’s back, between the shoulders, and down to the base of the tail. Part the hair at each spot until the skin is visible. 


  • Works on fleas and ticks.
  • Easy to use.


  • High price

Possible Side Effect 

  • Skin reaction on some dogs.

K9 Advantix II Tick and Flea Prevention for Small Dogs: Best For Application

Amazon’s Choice in Dog Flea Drops by K9 Advantix

Brand: Advantix

Item Weight: 1.6 ounces (45.36 grams)

Breed recommendation: Dogs

Size recommendation: Medium dogs 

Lifestage: All stages

Administration Form: Drops

Active ingredients: Imidacloprid 8.80%, permethrin 44.00%

Instructions for use: Read instructions on the product before application

About This Item

  • Bayer K9 Advantix II Tick and Flea prevention for medium dogs is a broad-spectrum, veterinarian-recommended flea and tick prevention that kills and repels mosquitoes, a feature not seen in many other fleas and tick solutions. 
  • Some flea and tick prevention treatments require a flea or tick to bite your dog to work, but K9 Advantix II Flea and tick prevention for dogs is a topical composition that works through touch, so the flea, tick, or mosquito does not have to bite your dog to die. 
  • One application of Bayer K9 Advantix II Flea and tick prevention for medium dogs kills fleas in as little as 12 hours, is waterproof after 24 hours, and kills fleas, ticks, and mosquitoes for up to 30 days, even after a wash or swimming. 
  • A grooming shampoo formulated exclusively for pets is advisable. Do not use K9 Advantix II on cats. Only use on dogs.


  • For 30 days, it keeps new fleas and ticks at bay.
  • It does not require a prescription and is suitable for dogs of any size.
  • It kills Existing fleas in approximately 12 hours.
  • Simple to use at home
  • Puppies seven weeks and older are safe to use.


  • It’s poisonous to cats and children. 
  • Irritation of the skin is possible.
  • You must reapply every month.

Possible Side Effect 

  • Irritation of the skin.

Triple Medium and Large Dog Wormer: Best For Different Worms

Amazon’s Choice in Dog Wormers by Durvet

Brand: Durvet

Item Weight: 0.81 ounces (22.96 grams)

Breed recommendation: Dogs

Size recommendation: Medium and large

Lifestage: All stages

Administration Form: Oral

Active ingredients: Pyrantel pamoate and praziquantel

Instructions for use: Use directions on the package

About This Item

  • These triple wormer tablets for medium and large dogs can treat seven types of worms, including tapeworms, roundworms, hookworms, and other parasitic worms.
  • The tablets are chewable.
  • There may be differences in packaging.
  • How to feed; give one 0.005oz (0.114gm) pill to a dog weighing 25.1 to 50.0 pounds (11.39 to 22.7 kilograms). Give two 0.005oz (0.114gm) tablets to a dog that weighs between 50.1 and 100.0 pounds (11.39 to 45.4kilograms). Give three 0.005oz (0.114gm) tablets for dogs weighing 100.1 to 150.0 pounds (45.4 to 68.1 kilograms) Give four 0.005oz (0.114gm) tablets to a dog weighing between 150.1 and 200.0 pounds (68.1 to 90.8 kilograms).


  • It’s effective and easy to administer.
  • Treats different types of worms


  • Tablets can cause choking.

Possible Side Effect 

  • May cause drowsiness.

PetArmor 7 Way De-Wormer for Dogs: Best For Medium Dogs

Amazon’s Choice in Dog Wormers by PetArmor

Brand: PetArmor

Item Weight: 0.32 Ounces (9.07 grams)

Breed recommendation: Dogs

Size recommendation: Medium

Lifestage: All stages

Administration Form: Solid

Active ingredients: Pyrantel pamoate

Instructions for use: Do not use this product on cats

About This Item

  • Treats and controls worms in dogs. Treats seven different types of worms: two kinds of tapeworms, two kinds of roundworms, and three kinds of hookworms.
  • These vet-quality tablets are appropriate for pups 12 weeks and older and small dogs weighing 6.0 to 25 pounds (2.72 to 11.35 kilograms).
  • PetArmor broad-spectrum dewormers are chewable tablets making them simple and convenient to administer to your dog.
  • Keep an eye on your dog for a few minutes after dosing to ensure that the dog did not reject the chewable dewormer and that it consumes the entire dose of dewormer. 
  • Read and follow the label instructions for the best results with any PetArmor dog dewormer. If your dog needs treatment, speak with your veterinarian and have a fecal test performed to rule out any other problems or parasites.


  • Ideal for 12-week-old puppies and small dogs weighing 6.0 to 25 lbs (2.72 to 11.35 kilograms). 
  • It contains pyrantel pamoate, which kills seven different kinds of worms.
  • Its protective packaging keeps the item safe from damage and moisture.


  • Causes dehydration.

Possible Side Effect 

  • Causes dehydration.

FAQs on Dog Wormers

What Happens if My Dog Already is Already Having Heartworms?

If your puppy or dog is already heartworm infested, you’ll need to set a treatment plan with your veterinarian. This includes calming down your dog and evaluating the severity of the heartworm infection.

Your veterinarian will next begin therapy, which may include injections, hospitalization, surgery, and other procedures.

Does My Dog Need Year-Round Protection Against Heartworms?

Even though mosquitoes are only present during certain times of the year, year-round heartworm prevention is recommendable. This protects your dog from stowaway insects in indoor situations or while on vacation.

Year-round preventative procedures protect microfilariae that may be dormant in your puppy’s system.

What Happens if I Miss a Dose of the Heartworm Preventive?

For total protection, you must give heartworm meds to dogs on a precise, unbroken schedule. If you forget to give your pet a dose, call your veterinarian and check the product information to determine if it’s still safe to give.

Your veterinarian may prescribe heartworm testing in six months, depending on the interval between doses.

Are There Risks Associated with Canine Heartworm Preventatives?

Every drug, including heartworm preventatives, has side effects. Because some breeds, such as members of the collie family, are sensitive to specific active chemicals in drugs, it’s always a good idea to check with your veterinarian first.

Because heartworm prevention medications require a prescription, your veterinarian will most likely discuss your options with you and help you make the best decision for your pet. They will also point out potential side effects, such as lethargy or stomach problems.

giving pill to a dog

Our Conclusion for Canine Heartworm Meds

Heartworm illness is a powerful foe, but happily, following a preventative practice can help your dog stay healthy and happy. Use our choice for the best heartworm prevention for dogs: Advantage II 6-Dose Large Dog Flea Prevention. It is the best for treating and preventing different types of worms.