Content Reviewed by an Essentials PetCare Veterinarian

The Basics

1. What: Heartworm is a parasite that causes irreversible lung damage and heart failure in dogs and cats.

2. Why: Heartworm infection may cause severe inflammation in your pet’s cardiovascular system, eventually causing lasting damage to the heart, lungs, and arteries. There is no cure for heartworm disease in cats, and it can be very difficult to treat in dogs.

3. When: All pets, including those on heartworm prevention, should be tested annually.

4. How: Ordinarily heartworm testing is conducted through a basic blood test.

5. EPC affordable price: Heartworm blood test for dogs: $25. Check in now.

What Is Heartworm?

Heartworm, also called  Dirofilaria immitis, is a parasitic roundworm that causes irreversible lung damage and heart failure in pets. It is transmitted by infected mosquitos.

Heartworm is a thread-like worm that may grow from 6 to 12 inches in length, clogging and causing critical inflammation in the pulmonary arteries of the lungs in both dogs and cats. Heartworm disease can be fatal.

Why Heartworm Affects Your Pet

Heartworm infection is a serious disease in dogs and cats. The worm produces unrelenting inflammation that damages the lining of the pet’s blood vessels, causing progressive thickening of the vessel walls, which leads to scarring, and ultimately irreversible damage to the pet’s cardiovascular system. The thickened and obstructed blood vessels go on to impair circulation and increase blood pressure, resulting in heart failure. Heartworm disease causes lasting damage to the heart, lungs, and arteries.

Heartworm Symptoms

According to the FDA, symptoms of heartworm disease may vary from:

Class 1:  No symptoms or mild symptoms, such as an occasional cough.

Class 2:  Mild to moderate symptoms, such as an occasional cough and tiredness after moderate activity.

Class 3:  More severe symptoms, such as a sickly appearance, a persistent cough, and tiredness after mild activity. Trouble breathing and signs of heart failure are common. For classes 2 and 3 heartworm disease, heart and lung changes are usually seen on chest x-rays.

Class 4:  Also called caval syndrome. There is such a heavy worm burden in these cases that blood flowing back to the heart is physically blocked by a large mass of worms. In caval syndrome, blood pressure changes cause worms to move from the pulmonary arteries into the right side of the heart where they become intertwined around the tricuspid valve, the valve separating the top of the right heart, atrium, from the bottom of the right heart, ventricle. Caval syndrome is life-threatening and quick surgical removal of the heartworms is the only treatment option. The surgery is risky and even with surgery most dogs with caval syndrome pass away.

Heartworm Disease Is Different in Cats and Dogs

Dogs are natural hosts for heartworms. This parasite thrives in dogs and is able to reproduce. A single dog may carry several hundred worms in its body and still appear well, making heartworm disease a silent killer. The quality of life in dogs that suffered with heartworm infestation is compromised even after treatment.

Cats are unusual hosts for heartworms, and typically just a couple of worms survive in a cat. This parasite is often unable to grow to adult stages in cats, which causes heartworm disease to go undiagnosed in felines. However, even microfilariae, heartworm larva, can cause severe infection, a condition known as heartworm associated respiratory disease, or HARD. Worse, cats have no treatment option for heartworm and an infection will eventually prove fatal. Cats will generally live between two and four years after they become infected with heartworms, according to the American Heartworm Society.

When Your Pet Needs Heartworm Testing

All pets, including those on heartworm prevention, should be tested at least annually. If a dog has not consistently taken heartworm prevention for the last 12 months, they should be re-tested in 6 months. Ordinarily heartworm testing is conducted through a basic blood test.

Dogs’ heartworm tests should be done during a routine visit for preventive care. Because it takes at least 6 months for a dog to test positive after it has been infected, adult dogs over 7 months of age and previously not on a preventive medication need to be tested prior to starting heartworm prevention. Then, they should be tested again 6 months later and yearly after that to ensure they are heartworm-free.

Puppies, under 7 months of age, can start heartworm prevention without a test. But they should be tested 6 months after the initial visit, tested again 6 months later, and yearly thereafter, as long as they are kept on monthly dosages of preventive heartworm medication.

Cats can be often misdiagnosed because it is difficult to detect heartworms in felines. Veterinarians will normally need a blood test along with an x-ray or ultrasound to look for heartworm infection in cats. However, because most heartworms don’t develop to the adult stage in cats, testing is not as straightforward in cats as it is in dogs. Similar tests that are used in dogs, called antigen tests, are used in cats, along with another type of blood test, known as an antibody test. Unfortunately, both of these can be positive or negative in cats that have heartworm infection making a definitive diagnosis difficult. Cats do not have to be tested before starting prevention but may need testing at the veterinarian’s discretion to evaluate exposure and risk. Prevention is critical because of the lack of an approved treatment for heartworm disease in cats.

Kittens should get started on a heartworm prevention routine as early as the product label allows and no later than 9 weeks of age.

In some areas, testing twice each year may be needed, particularly in pets that are exposed to high numbers of mosquitoes for long periods of time.

How Heartworm Can Be Prevented

Prevention is by far the best option for keeping your pet free of heartworms. Pets can be put on a monthly schedule for pills, chewables, or topical medication to be applied on the pet’s skin. There is also a 6-month and a 12-month injectable product. Pet parents should discuss with the veterinarian the best options for their pets. A year’s supply of heartworm preventive medication will cost about $35 to $80, depending on a pet’s weight. This investment is well worth it!

Puppies and kittens are bound to grow fast during their first 6 months on preventive care, and pet parents must follow the veterinarian’s dosage prescription to cover the change in body weight. It is also crucial to be on top of your pet’s monthly medication and regular testing to make sure she is protected against heartworms.

Essential Tip: Puppies, kittens, and cats can receive a heartworm prevention prescription with a doctor’s exam at Essentials PetCare. Check in now.

How Heartworm Is Treated

There are a few routes of treatment for heartworm in dogs with the goal of eliminating larva, known as microfilariae, and adult heartworms. These treatments may include antibiotics, corticosteroids, Melarsomine, and prevention products to both remove the microfilariae and prevent further infection. In severe cases in which heart failure has already developed, cardiac medications such as diuretics, vasodilators, and positive inotropic agents may be needed to stabilize the patient before treatment to remove the heartworms can be initiated. These cases always carry a much more guarded prognosis for survival.

Heartworm Treatment Protocol

The American Heartworm Society has organized a thorough treatment protocol for dogs with heartworms, which has been proven to be safe and effective. This standard treatment consists of pre-treatment with an antibiotic called Doxycycline for four weeks, followed by multiple injections in the muscles of the lower back using Melarsomine, the only FDA-approved drug to treat heartworms. The medication is typically administered as a single injection, with two additional injections one month later, given 24 hours apart.

The standard plan incorporates blood tests and chest x-rays before the injections are given to ensure that your dog is healthy enough for the treatment. Therefore, the pet should be admitted to a full-service veterinary hospital. The drug Melarsomine is expensive, driving care costs, which typically average between $500 to $1000, or even more, depending on the size of the dog and the amount of drug required.

Download here the American Heartworm Society standard treatment plan, which is the only FDA approved treatment for canine heartworm disease.

Alternative Heartworm Treatment Protocol

In cases when standard treatment is cost-prohibitive, Essentials PetCare is able to offer an alternative treatment protocol. This protocol is based on research showing the clearance of adult heartworms using a combination of the antibiotic Doxycycline and a monthly heartworm and flea prevention medicine called Advantage Multi. 

The alternative protocol does not clear the worms as rapidly as the standard therapy, thus ongoing inflammation and damage can occur to the heart and lungs while waiting on the worms to clear. However, this protocol is often chosen due to the lower cost and is certainly preferred over no treatment at all. This is also preferred to using a heartworm preventive alone, a protocol performed in the past and known as slow kill. Unfortunately, slow kill can take over two years to be effective and, in some cases, it has been linked to development of resistance to heartworm preventive products.

Studies published by several peer-reviewed journals have shown this alternative protocol to be over 90% effective in removing heartworms. This is similar to the success rate of standard Melarsomine therapy, which has been shown to be 95-98% effective in removing worms.  However, this also means there will be some cases in which the worms are not completely removed. Hence, there is no guarantee that this protocol will be 100% effective.

Pets undergoing the alternative treatment, must observe the following instructions:

  • All medications must be administered as directed and all instructions followed in order to give the dog the best chance of a successful recovery.
  • Highly aerobic activity such as long runs, fetch games, ball chasing, and the like should be avoided, while the dog is undergoing treatment.
  • Doxycycline should be administered with food to help avoid gastrointestinal side effects.
  • Advantage Multi should be applied on a strict schedule every 30 days. The hair between the shoulder blades should be parted and the product applied directly to the skin, never on top of the hair coat.
  • If the dog acts like the application of Advantage Multi causes any irritation, the pet should be engaged during the initial 1 to 2 hours after application with activities such as petting or chew toys. The irritation will subside once the product has dried.
  • Re-test every 6 months, during the treatment protocol for monitoring and prescription refills.
  • Pets should be closely monitored for any signs of respiratory problems like coughing, increased respiratory rate or effort, weakness, or collapse. The veterinarian should be called immediately if any of these signs occur. 

Essential Tip: Essentials PetCare offers this affordable Alternative Heartworm Treatment Protocol for dogs suffering with heartworm infection. Check in now.

Palliative Heartworm Treatment for Cats

Although a treatment for heartworm in cats is not yet available, your veterinarian can help stabilize the pet and create a long-term management plan. Periodic blood tests and x-rays or ultrasounds should continue every 6 to 12 months, as recommended by the doctor. A steroid, like Prednisone, may be prescribed to help reduce inflammation. Intermittent hospitalization may be necessary to administer therapy, including drugs to treat the lungs and the heart, intravenous fluids, and antibiotics. Surgically removing heartworms may be an option as well, but this procedure carries an even higher risk in cats than in dogs.


The visit to collect blood from your pet for heartworm test at Essentials PetCare takes 15 minutes on average. Our team will have the results for you on the same day!


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