How to Treat Heartworm in Dogs

How to Treat Heartworm in Dogs
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vet verified PetCareRx Staff Veterinarian DVM

If your dog is diagnosed with heartworm disease, he/she can likely recover fully with treatment. Learn about the different treatment options available here.

Heartworm disease can cause a lot of harm to your dog and is potentially fatal. The good news, though, is that treatment of heartworm in dogs is generally both possible and likely to be successful. Heartworm treatment is a fairly involved and lengthy process, and so it is best to give your dog a monthly heartworm prevention medicine like Trifexis to avoid them getting heartworm.

In most cases, heartworm is treated through a two-pronged operation: In one treatment, adult heartworms are killed, and in another, the microfilaria, or baby heartworms, are killed. The order of these treatments varies and may be determined by the health of your dog. Veterinarians will also prescribe heartworm medicine like Interceptor, which attacks Wolbachia, which is itself a parasite attached to heartworms.

Destroy Adult Heartworms

Adult heartworms – which can occupy the heart, lungs, and blood vessels – are killed with an adulticide. Melarsomine dihydrochloride, an arsenic-based poison, is sold under the name Immiticide.

For the treatment, dogs are given a series of three injections of Immiticide administered by a veterinarian. Following each injection, dogs need rest and recuperation. During the recuperation period, dogs must rest and not exert themselves because exercise can be fatal at this point. Keep your dog safe after receiving a miticide injection by having them be leash walked for the following six months. Mass quantities of heartworms are killed by the adulticide treatment, and these heartworms need to be safely absorbed. Since adult heartworms are present in the heart, there is a danger of an embolism or blocked artery as the heartworms are destroyed. Inactivity reduces this risk, allowing the worms to be absorbed slowly. The other two doses of Immiticide are also given by injection. Generally, doxycycline is also given along with the adulticide to eliminate the Wolbachia parasite.

Eliminating Microfilaria

In addition to getting rid of the adult heartworms, veterinarians will also attack the microfilaria using Ivermectin, which can also be used for heartworm prevention for dogs. Generally, using preventatives when there is a known infection is unsafe since killing many worms at once can overwhelm a dog. Since Ivermectin kills microfilaria slowly, the danger is averted.

Slow Kill Method

While not generally recommended, another method of handling heartworms is to only attack the microfilaria, leaving existing adult heartworms to die of natural causes. This is known as the slow kill method. It’s cheaper and does not require a rest period and debilitating adulticide. However, adult heartworms are innately dangerous to dogs, and complications from their presence within your dog could occur.


In extreme heartworm cases, dogs may develop Caval syndrome, with heartworms filling and then expanding out of the dog’s heart. If your dog develops this syndrome, surgery will be required to remove the worms. This is a more invasive and dangerous treatment and should only be done for dogs who will otherwise not survive.

When it comes to this problem, prevention is the dog heartworm med. Learn more about preventing heartworm here.

Heartworm Tests Explained

While dogs in warm climates with an active mosquito presence are particularly vulnerable to heartworm disease, the infection has been diagnosed in every state (even Alaska). In the early stages of the disease, your dog may not show any symptoms at all. Or your pet may have relatively minor symptoms – a cough or a reluctance to exercise – that could easily be mistaken for an inconsequential illness.

Are Heartworm Tests Necessary?

Given the risks of missing or misdiagnosing the early symptoms of the condition, veterinarians generally test dogs for heartworm disease annually. The test is a good backup option in case a preventative treatment dose was accidentally skipped. Regular testing helps ensure that the disease is caught early on when treatment options are easier and more effective.

A more serious reason for testing for heartworms before preventative treatment is the dog’s health. In addition to killing larvae, preventatives will also destroy the microfilaria (baby heartworms born to adults). A sudden, en masse destruction of all the microfilaria could have a negative, or even fatal, impact on a dog’s health. Even without a negative health impact, dosing preventatives to a dog with an adult heartworm infection could mask the seriousness of the disease’s presence and development, delaying treatment.

How Is Testing Done?

To test for the presence of heartworms, your vet will take a small blood sample from your dog and use this for one of these types of tests:

  • Antigen Test– Veterinarians will check for antigens left within the bloodstream by the female heartworm.
  • Microfilaria Test – In Knott’s test, vets are looking for the presence of microfilaria, or the young heartworms, within the dog’s blood. Another microfilaria detection test is known as a Difil test.

Both of these blood tests have a small risk of a false negative; that is, there is a possibility that the tests will report that your dog does not have heartworm when in fact, the dog does. This is particularly true if your dog’s heartworm case hasn’t progressed to the point where adults are present, if there is a low number of worms, or if your dog is only infected with male heartworms.

Sometimes the two types of blood tests are done in conjunction, particularly if your vet suspects that the test results are incorrect. When dogs test positive for heartworms, x-rays of the lungs can be done to inspect for signs of the disease’s progress.

When to Test for Heartworm

Heartworm tests should be administered every year because of the long inculcation period as heartworms mature. After mosquitoes transmit the heartworm larvae to dogs, it takes between six and seven months for the parasites to develop and infiltrate into the dog's bloodstream. While the larvae are developing, the disease is undetectable. When a dog is tested, generally in the early springtime, the test will determine if the dog picked up the disease during the preceding warm mosquito season.

Heartworm Disease Can Be Treated 

Heartworm disease is a serious condition but can be treated in dogs if caught early enough. Heartworm disease is transmitted through mosquitoes by the heartworm parasite. This worm-like organism enters the dog's bloodstream and grows inside the heart, lungs, and arteries. Heartworms can cause major damage to these organs and lead to death if not diagnosed or treated quickly. Because it's a preventable disease (you can protect your dog from mosquitoes), we strongly recommend that you protect your pet with regular heartworm meds for dogs.

There Is No Known Cure 

There is no known cure for heartworm disease. Treatment is aimed at controlling the disease and easing discomfort and symptoms. If a dog's heartworm infection is not treated, it can cause serious or life-threatening damage to the lungs and other organs, including kidney failure.

Heartworm pills for dogs cost between $12 and $20 per month, depending on the type of medication used and the size of your dog's body weight. Some examples are Interceptor Plus, Sentinel Spectrum, and Heartgard Plus.

Heartworm treatment can be painful. Some medications require monthly injections into your dog's abdomen or neck area; these shots are often painful for dogs to receive, which may make them reluctant to participate in this part of their treatment plan without sedation.

Proper Schedule

It's important that you give your dog heartworm medication on the proper schedule according to the manufacturer's directions. Heartworm prevention prescriptions are usually given once a month, but if your pet has been infected and is receiving treatment for heartworms, it may need the medication more frequently.

Some medications require you to apply them to the skin, while others are ingested orally with food. Make sure that you follow these instructions carefully so that your dog receives the correct dosage and does not experience any adverse reactions. In addition to following these guidelines closely when administering prescription medications, here are some other things you should know about taking care of your pet:

  • Never give more or less than what is recommended by your veterinarian
  • Give medication at regular intervals throughout each day if possible

When it comes to your dog's health, best to be safe than sorry. If you suspect he may have heartworm disease, contact your veterinarian right away. The sooner you get him treated, the better chance he has at recovery!

Frequently Asked Questions

How long does it take to cure heartworm in dogs?

The treatment of heartworm disease in dogs can be a lengthy and complex process that typically takes several months. The duration of treatment will depend on the severity of the infection and the dog's overall health. Generally, the treatment process involves several stages. First, a veterinarian will assess the dog's overall health and the extent of the infection. They may also perform tests to determine the stage of the disease. Next, the dog will typically receive a series of injections to kill the adult heartworms. These injections are usually given over a period of several weeks and require close monitoring by the veterinarian. Following the injections, the dog may be given medication to help kill any remaining heartworms and prevent new infections from developing. This medication is typically given for several months. Throughout the treatment process, the dog will need to be closely monitored by a veterinarian and may need to be restricted from exercise or other strenuous activities. After treatment is complete, the dog will need to undergo follow-up testing to ensure that the infection has been fully resolved.

Can you see heartworms in dog poop?

No, it is not possible to see heartworms in dog poop. Adult heartworms typically live in the heart and lungs of infected dogs, and microfilariae (immature heartworms) circulate in the bloodstream. They are not passed out in feces. Testing for heartworm disease involves checking a blood sample for the presence of heartworm antigens or microfilariae. A veterinarian can perform this test and can also examine the dog's heart and lungs using radiography or ultrasound to determine the severity of the infection.

How contagious is heartworm among dogs?

Heartworm disease is not directly contagious from one dog to another. It is transmitted by the bite of an infected mosquito that carries heartworm larvae. When the mosquito bites a dog, the larvae enter the dog's bloodstream and eventually migrate to the heart and lungs, where they develop into adult heartworms. However, multiple dogs in the same household or community can become infected with heartworms if they are bitten by infected mosquitoes in the same area. Therefore, it is important to use preventative measures to reduce the risk of mosquito bites, such as keeping dogs indoors during peak mosquito hours and using mosquito repellent. Heartworm disease can be prevented with regular administration of a heartworm preventative medication, which is highly effective at preventing infection. Therefore, it is recommended that all dogs receive regular heartworm prevention medication, even if they are not showing any symptoms of heartworm disease.

What happens if you give a dog heartworm prevention that already has heartworms?

If a dog that already has heartworms is given heartworm prevention medication, it can potentially have serious consequences. This is because heartworm prevention medication is designed to prevent the development of new heartworm infections, but it does not treat existing infections. In some cases, an ivermectin-based heartworm preventive may be used as part of the treatment protocol for heartworm-positive dogs. However, this approach is typically used only in certain cases and under close veterinary supervision. When used as part of a heartworm treatment protocol, the ivermectin-based medication is typically given at a higher dose than the preventative dose and is used in conjunction with other medications to help kill adult heartworms.

Can dogs recover from heartworms without treatment?

It is unlikely that a dog infected with heartworms will recover without treatment. Heartworm disease is a serious condition that can cause significant damage to a dog's heart, lungs, and other organs. Over time, the infection can become more severe and can lead to serious health problems, including heart failure and even death. While some dogs may show no symptoms or only mild symptoms of heartworm disease, it is important to remember that the infection can progress over time, leading to more severe symptoms and complications. Therefore, it is important to have your dog tested regularly for heartworms and to follow your veterinarian's recommendations regarding heartworm prevention and treatment. Treatment for heartworm disease can be complex and lengthy, but it is often necessary to ensure that your dog recovers fully and has the best chance of a healthy life.

Related Content

Heartworm Disease in Dogs: 5 Things You Should Know
Heartworm Symptoms
Heartworm Medicine
How to Prevent Heartworm in Dogs

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis, or treatment by, your veterinarian. Always seek the advice of your veterinarian or other qualified professionals with any questions you may have regarding a medical condition. Never disregard or delay seeking professional advice due to what you may have read on our website.

Heartworm Preventatives

Heartgard Plus
Iverhart Max
Tri-Heart Plus

Related Content

Heartworm Medicine
How to Prevent Heartworm in Dogs
Heartworm Tests Explained

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis, or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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