What You Need to Know About Heartworm in Dogs


Bryan Huynh

- Updated February 21, 2024

What You Need to Know About Heartworm in Dogs

Heartworm is a serious condition that can bring your dog a lot of pain, discomfort, and even have long-term effects if left untreated. But don't worry, we've got you covered with all the important information you need to know about taking care of your furry buddy when it comes to heartworm.

In the sections below, we'll break down everything from prevention methods to common symptoms, diagnosis, treatment options, and more. It's crucial to stay informed and proactive to keep your dog safe and healthy. And remember, having pet insurance can provide an extra layer of financial support when it comes to tackling heartworm and other health issues. So let's dive in and ensure your pup stays heartworm-free and happy!

Heartworm: What It Is

Heartworm is a serious -- sometimes fatal -- disease caused by a parasitic worm (Dirofilaria immitis) and spread through mosquito bites. The worms live in the heart and pulmonary arteries, travel through the bloodstream, damaging vital organs and arteries, and (six months after being infected) end up in the heart chamber and vessels of the lung. It can result in lasting damage and eventually cause lung disease, heart failure, kidney failure, liver failure, other organ damage, and death.

Heartworm can affect several animal species -- dogs, cats, ferrets, coyotes, foxes, wolves, and more. There can be several hundred worms living in a dog at one time, with life spans of five to seven years. Dogs of all breeds (and other animals) need to be carrying male and female heartworm before they can reproduce and produce offspring called microfilariae. These larvae enter the bloodstream and are taken by mosquitos before becoming infected in the following two weeks; they then pass onto dogs and other animals through mosquito bites.

While these heartworms may start off as minuscule larvae, they can eventually end up over as thin noodle-like worms over a foot long. It takes around 6 months for heartworms to grow fully, and they can live an average of 5 to 7 years.

Heartworms can infect dogs no matter where you live, although they have a larger population in certain parts of the US depending on temperature (hot and humid climates) and other environmental factors (coastal regions and river tributaries specifically) or increase depending on the year. Wild animals such as coyotes can be carriers of heartworm in residential areas, causing the number of infections to increase.

Heartworm is mosquito-borne: it isn't spread from dogs to other mammals so it can't be spread to you (note: there are rare cases in which humans get heartworm from mosquito bites).


Dogs don't typically show symptoms of heartworm infection for the first few months; however, the more active your dog is, the more likely they are to deal with the symptoms of heartworm earlier. These symptoms include:

  • Difficulty breathing
  • Coughing
  • Lethargy
  • Loss of appetite
  • Fatigue after moderate exercise
  • Weight loss
  • Vomiting
  • Bulging ribs
  • Swollen abdomen due to fluid buildup

In some cases, dogs won't show any symptoms of heartworm until the late stages of the infection. Many dogs may not show any signs of heartworm unless they face a temperature or environmental change.

If you notice your dog has pale gums, dark urine, and has trouble breathing, take them to the vet immediately, as these are signs of caval syndrome, or a sudden blockage of blood flow in the heart that leads to cardiovascular collapse. It's essential that they receive surgical removal as soon as possible to have a chance of survival.


These symptoms can also be similar to other illnesses, making it potentially difficult to diagnose. Additionally, the severity of the symptoms doesn't necessarily correlate with the severity of the heartworm infection. It's essential that you make an appointment with your veterinarian immediately to know for sure and receive the proper treatment, if necessary.

In order to test for heartworms, your vet will draw a blood sample from your dog to check for heartworm proteins. If your dog has a positive test, your vet may have you follow up with more tests for your dog (such as an additional heartworm test or echocardiography, X-ray, or ultrasound) or begin treatment immediately.

Whether the testing is done in the hospital or sent to a lab, you'll receive results quickly.


When it comes to treating heartworm in dogs, your vet wants to be absolutely certain before starting the treatment process. This is because the treatment can be time-consuming and costly.

If your dog tests positive for heartworm, your vet will first focus on stabilizing their condition. Once your dog is stable, the vet will proceed with administering the necessary treatment to eliminate the worms. The goal is to minimize any major side effects or risks associated with the treatment.

During the treatment period, it's important to restrict your dog's exercise and physical activity. Rest is crucial because the presence of heartworms can lead to blockages in the blood vessels near the lungs. If your dog's heart rate increases, it could result in serious complications, even fatal ones like a pulmonary embolism. So, it's absolutely vital to ensure that your dog avoids any strenuous activities. In some cases, vets may prescribe a sedative to help keep your dog calm and relaxed during the treatment process.

Until your dog is fully healed, you can occupy them by introducing them to new toys or by being near them for pets and cuddles whenever you're at home to keep them from being lonely. Keep them in a large crate or room when you're not at home, and go for a short, slow-paced walk when they need to use the bathroom.

Heartworm treatment requires an injection of Immiticide or Diroban that is given two to three times and may be followed by Advantage Multi for Dogs (to get rid of heartworm larvae from your dog's bloodstream), antibiotics, or steroids. In most cases, dogs will fully recover. In serious cases, your veterinarian may perform surgery on your dog to remove the heartworms physically.

Your dog will still have to be tested up to 6 months after treatment to ensure that they were eliminated entirely.

Heartworm Treatment Costs

Heartworm treatment costs typically range from $500 to $1,000, depending on the severity of the illness, testing done, and treatment administered.

Pet insurance can cover some -- or even most -- of the costs of treatment. (Looking for a pet insurance plan? Look to our top providers to learn more.



Whether your dog has had heartworm or not, they should begin taking a monthly heartworm preventative medication. Prevention is key -- even if your dog has just finished treatment.

Your vet can either prescribe you a chewable pill or a topical medication to prevent heartworm (and potentially other intestinal parasites). The dosage you give your pup depends on their weight.

Puppies under 7 months can be given preventative medication without a blood test; however, older dogs need to be tested before taking this medication. It's essential that your dog is tested 6 months after beginning their heartworm prevention routine and then annually after that. Prevention is effective, but if your pet spits out the heartworm pill or rubs the topical medication off, you'll want to know whether your dog needs further treatment.

You can also help your dog avoid getting heartworm by applying mosquito repellents while outdoors, avoiding peak mosquito times (dusk and dawn), and getting rid of any spots that mosquitos may swarm to such as standing water. 

What is heartworm in dogs?

Heartworm is a disease caused by a parasitic worm called Dirofiliaria immitis, and is spread through mosquito bites. This serious condition can result in lung disease, heart failure, organ damage, and even death.

What are the first signs of heartworm in dogs?

Some of the first signs of heartworm include a persistent cough, fatigue, decreased appetite, and weight loss. Later stages of heartworm may result in heart failure and a swollen abdomen due to excess fluid.

Can heartworm be cured?

Most cases of heartworm can be treated, especially if caught early.

About The Author

Bryan Huynh

Bryan Huynh

Product Tester & Writer

Bryan Huynh is a dedicated Product Tester & Writer. Just as insurance has your back, Bryan works to review and inform you about the wide range of insurance products available, ranging from business, auto, health, home, pet, to life insurance.

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