Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Dog laying in grass

The essentials

  • Heartworm disease is not contagious among dogs — Dogs cannot catch heartworms from one another, it’s only spread by mosquitoes.
  • Heartworms take about six months to mature and can live in a dog’s body for up to seven years — Worms cause inflammation and damage a dog’s lungs, arteries, and heart if left untreated.
  • Prevention is your best line of defense — There are treatments to fight heartworms, but it’s best to take preventative measures, like giving your dog monthly heartworm medication.

While it has been diagnosed in all 50 states, heartworm disease is extremely prevalent in humid, warm places where mosquitoes abound. Heartworm prevention is the best measure to protect your dog from this potentially dangerous disease.

However, there are treatment options if your dog does get diagnosed. Here’s a breakdown of treatment options and how much they cost, including which expenses pet insurance may help cover.

What is heartworm disease in dogs?

Heartworms, scientifically known as Dirofilaria immitis , are harmful parasites transmitted by infected mosquitoes. While heartworms can affect many mammals — including cats and possibly but rarely humans — our canine friends are often a favorite host for infected mosquitoes. 

Heartworms can grow up to 12 inches long. These noodle-like parasites damage a dog’s vital organs, causing heart blockages and obstructing blood vessels. 

Mosquitoes only transmit heartworms in their larval stage. Heartworm prevention works by killing these young mosquitoes before they have the chance to grow into the adult parasites that wreak havoc. Heartworm prevention does not kill adult heartworms. Therefore, if a dog is diagnosed with heartworms, they’ll need further medical treatment than a preventative.

How are heartworms spread?

Heartworms aren’t transmitted between canines or even between dogs and cats. The only way for a dog to acquire heartworm disease is to be bitten by an infected mosquito. Even then, if they’re on heartworm prevention , the larvae will most likely be killed before they have the chance to grow into the malignant adult heartworms that cause disease.

Symptoms of heartworm in dogs

Signs that your dog has heartworm disease may not be apparent until well after an infected mosquito has bitten them. This is because it takes about six months for infected larvae to mature fully and for your dog to start showing symptoms of an infection. Heartworm symptoms are broken up into four classes, including:

  • Class one. Early-stage clinical symptoms of heartworm disease are uncommon. At most, you may notice your dog has a mild cough in this phase.
  • Class two. As the infection progresses to class two, you may notice your dog has a more persistent cough, and their exercise tolerance may be limited.
  • Class three. More symptoms present in this class, including decreased appetite and weight loss, increased exercise intolerance,  abnormal lung sounds, swollen belly, fainting, and weak pulse.
  • Class four: This is the most severe stage of the infection, often called Caval syndrome. It often indicates a particle blockage due to worms in the heart and major blood vessels. Your dog may exhibit symptoms of a cardiovascular collapse, which include pale gums, dark urine, and severe difficulty breathing.

What about cats? 

Most cats who are bitten by an infected mosquito combat heartworms on their own. A feline’s body isn’t as hospitable to these parasites, so most larvae die before they have the chance to mature. 

Unfortunately for reasons we don’t understand, some cats still develop heartworm disease. At the moment, there isn’t an approved treatment for heartworm disease in cats. If you live in a mosquito-heavy area, ask your veterinarian about putting your cat on heartworm prevention.

Diagnosing heartworm

Diagnostic testing for heartworm is usually done once a year at your dog’s annual exam. If you suspect your dog is infected with heartworms, it’s essential to get them tested by your veterinarian as soon as possible for the best prognosis. 

Vets commonly run two blood tests to check for heartworms. An antigen test can detect adult worms, while a microfilariae test identifies heartworm offspring.

  • An antigen test can see if there are any antigen proteins in your dog’s blood, which are released by adult female heartworms. This test can detect if your dog is infected with heartworms about five months after being initially infected. 
  • Another standard blood test to check for heartworms is to look for microfilariae in blood work. Microfilariae, the heartworm’s offspring, can’t be detected until about six months after your dog’s been bitten by an infected mosquito. It takes that long for heartworms to mature and reproduce.

Heartworm testing and how much it cost

Type of test How Soon it Detects Heartworms Cost (Private Animal Hospital) Cost (Shelter or Rescue)
Antigen Test 5 months after initial bite $35-$75 Included
Microfilariae Test 6 months after initial bite $20-$40 Included

Additional testing

Additional tests to determine the severity of a dog’s heartworm and stage vary in price. An echocardiography costs around $575 on average. X-rays cost anywhere from $75-$500, and additional blood tests range from $100-$200. If an electrocardiogram is necessary, this costs anywhere between $725 and $1,000.

Additional testing

Test What It's For? How Soon It Detects Heartworms Cost Range
Echocardiogram Heart ultrasound to test for adult heartworms. Adult Stages $250-$350
Chest x-ray or radiograph Heart x-rays note enlargement or swelling in the pulmonary artery, suggesting heartworms. Adult Stages $75-$500
Additional blood tests A complete blood count test (CBC) detects heartworm-related problems in the blood, kidneys, or liver. 5 Months and Up $100-$200
Electrocardiogram Electrocardiograms help diagnose heartworms by recording unusual heart rhythms. Adult Stages $25-$65

What does pet insurance cover?

Treatment for heartworm disease will likely be covered as long as it isn’t a pre-existing condition. Heartworm prevention is different, however, since it’s considered a part of routine care. Unless you purchase a separate wellness plan, heartworm prevention and testing will likely be an out-of-pocket expense.  

👉Veterinary exam fees are covered by pet insurance. Find out exactly what is (and isn’t) included in heartworm testing and treatment by reading our pet insurance coverage guide.

Treatment and medications

There are typically four treatment steps: weakening adult heartworms, eliminating their growth, restricting your dog’s activity, and then preparing the dog for the medication used to kill the adult heartworms. A veterinarian will determine the best course of treatment depending on the stage of the disease.


Your vet will create a treatment plan for your dog depending on the stage of the heartworm infection and your dog’s health history. Some of the most common medications used to treat heartworm disease include:

  • Melarsomine. ($500-$1,500) Melarsomine is an antiparasitic used to treat heartworm disease by a series of injections. Due to it being derived from an organic arsenic compound, this medication comes with increased risks. Still, the American Heartworm Society’s guidelines recommend it since it kills more than 98 percent of worms during treatment.
  • Doxycycline. ($85-$110 for 30 pills) An antibiotic, doxycycline is usually administered during the first month of treatment either with or to prepare for the use of melarsomine. It’s been proven to weaken adult heartworms by killing the amoeba on the worms called Wolbachia.
  • Heartworm prevention. ($6-$18 per month) This will be administered on the first day and should be continued for the remainder of the dog’s life to stop the current infection and as a preventative.
  • Steroids. ($40 for 30 day supply; $50-$150 single injection) Steroids are often prescribed during and after your dog’s treatment to help reduce inflammation and blood clots.
  • Surgery. In severe cases, surgery may be required to remove and treat heartworm disease.

Heartworm medications

Timing Cost (Private Animal Hospital) Cost (Shelter or Rescue)
Preventative Heartworm Pill Lifetime $6-$18 (per month) $6-$18 (per month)
Melarsomine Series of injections during treatment $500 - $1,500 $500 - $1,500
Doxycycline 1-28 days $85 - $110 $85 - $110
Steroids 1 month $40 for 30 day supply or $50-150 single injection $40 for 30 day supply or $50-$150 single injection

👉 Heartworm prevention doesn’t kill adult heartworms. If your dog is diagnosed with heartworm disease, they’ll need heartworm treatment in addition to routine prevention to reduce their chance of reinfection.

Keeping dogs comfortable during treatment

While your dog is being treated for heartworm, it’s important to keep them comfortable and relaxed. Rest is vital to your dog’s recovery, so you’ll want to have items on hand to restrict their exercise for four to six weeks after their final melarsomine injection. Some equipment you may want to have include:

  • Crate or playpen. Though it may seem like a punishment, using a crate or playpen to restrict your dog’s activity during and after treatment will help them heal and get stronger.
  • Thundershirt. Treatment may be stressful for both you and your pup. To help ease your dog’s anxiety, try a thunder shirt to provide extra comfort and reassurance.
  • Puzzle toys. Dogs need to take it easy while being treated for heartworm, so they’re bound to become restless. Treat them with a frozen Kong or serve their meals using snuggle mats or dog puzzles to keep them entertained during recovery.
  • Bones and chews. In addition to dog puzzles and Kongs, try keeping your dog entertained with bones and chews while they recover.
  • Keep a leash on hand. While your pup recovers, always use a leash during the rest period to help limit their activity.


Your dog should be re-tested for heartworm disease six months after their final successful treatment. Like the tests used to detect a heartworm infection initially, your vet will conduct blood tests to make sure all of the worms were killed during treatment.

If the initial test comes back positive, they may need to run a confirmatory test to determine a true positive. If your dog tests positive for heartworms, your dog will need to undergo treatment again using melarsomine.

Complications and long-term costs

Though there are treatments to fight heartworm disease, it’s not always easy to rid your dog of the infection. It’s estimated heartworm treatment costs anywhere between $600 to $6,000. Even more, heartworms cause long-lasting complications even after they’re gone. Some of the most common long-term complications include:

  • Caval syndrome. This usually occurs during the final, 4th class of heartworm infection and requires surgery. It’s brought on by a heavy concentration of worms obstructing blood flow back to your dog’s heart. If left untreated, it can lead to heart, liver, and kidney damage and potentially death.
  • Lasting damage. Studies have shown long-term damage in dogs from heartworms, even after successful treatment. Some of these findings include discovering mummified heartworm remnants and continued vascular and pulmonary issues.

Heartworm prevention

The best preventive medication to help protect your dog from contracting heartworm disease is monthly heartworm medication. In addition, make sure to take your dog to the vet once a year for their annual check-up, including heartworm testing. If you’re worried about veterinary or treatment costs, pet insurance is a wise investment to help ease the burden of unexpected vet bills.

Frequently asked questions

How much does a heartworm test normally cost?

On average, tests to detect heartworm disease cost $45 to$50. The antigen test can detect as early as five months and costs between $35 and $75. The microfilaria test costs a little less — usually $20 to $40 — but only detects after six months after the initial mosquito bite

How much does it cost to treat a dog with heartworms?

Since treatment protocols for heartworm vary and depend on the severity of the infection, your dog’s medical history, and weight, the cost can vary. On average, it’s estimated heartworm treatments cost between $600 to $6,000 with your dog’s weight being the biggest factor.

Can I give my dog heartworm medicine without testing?

No. Heartworm treatment is a series of injections and a risky process that requires the guidance of a veterinarian. You will need to work with your veterinarian to diagnose and determine the best plan of action for treatment.

What to do if I can’t afford heartworm treatment?

Vet bills can pile up, but don’t let this fear keep you from taking your pup to the vet. If you’re concerned about cost, see if you qualify for CareCredit. In addition, pet insurance can help offset vet and unexpected emergency bills. It’s important to enroll your pup early, though, since most policies don’t cover pre-existing conditions. 

Do dogs make a complete recovery from heartworm disease?

While heartworm disease is potentially fatal, most dogs who receive treatment early have a good chance of making a full recovery. Since most dogs don’t show clinical signs until class 2 or later, heartworm prevention and annual heartworm screening are essential to catch and treat the disease before it causes permanent damage.