Heartworm Is A Silent Disease For Dogs, Here’s What You Need To Know About It


Pet Expert & Writer

Healthy, Natural Pet Food

20% off your first month! Use the Code: BLOG20
*valid for new signups only
20% Off!

Doggos tend to be man’s best friend with a heart of gold (obviously not literally). But besides being where they store their love for their favourite hooman, hobbies and treatos, it could also be a living and breeding ground for heartworm.

A heartworm is exactly as it sounds. When this parasitic roundworm (Dirofilaria immitis) matures into adult worms, they would look like 5 to 12-inch cooked spaghetti living in your doggo’s heart.

Image Credit: Humane Society of Tampa Bay


During their infestation, they would make themselves at home in your dog’s muscles, blood vessels, the pulmonary artery and heart. As a foreign and parasitic entity, the worms would cause inflammation and damage to the heart, arteries and lungs.

How Does A Dog Get Heartworms

These pesky noodle-like buggers worm their way into your dog’s healthy body via a carrier mosquito.

Residue from the mosquito’s bite contain immature worms called microfilaria is transmitted to your dog during a blood meal. These immature worms then make their way to the right side of the heart through the bloodstream.

After 6 months, these worms would mature, mate and live on for about 7 years. Hence after about a year, a dog may be a host to a colony of these worms.

Symptoms of Heartworm Disease

Like most health issues in dogs, the symptoms and effects on their general health and well-being comes in stages. 

Heartworm disease in dogs is often known as a silent killer because usually dog owners would overlook the symptoms until it’s too late. 

Early-Stage Symptoms

These would be the tell-tale signs that your doggo might have heartworms.

  1. Persistent dry coughing that’s induced by even small amounts of exercise as the parasites have made their way into the lungs creating blockage and discomfort.
  2. Lethargy, loss of interest in going for walks or being active as these worms affect the blood and oxygen flow which subsequently makes any form of physical activity too strenuous for your doggo.
  3. Loss of appetite even towards their favourite meals and treats as it may be too tiring for them to eat. This then causes rapid weight loss and starves their body of required nutrition.

Middle-Stage Symptoms

At this stage, the heartworms would have matured, increased their population and spread to the lungs and veins of the host causing severe blockage.

  1. Breathing difficulties that mimic an asthma attack as the blood vessels in their lungs are compressed by surrounding fluid build up (due to the inflammation) and thus reducing the rate of blood oxygenation.
  2. Bulging ribs due to fluid buildup in the lungs and weight loss.

Late-Stage Symptoms

The symptoms of the early stages would be amplified and coupled with more health complications due to the lack of nutrition, hydration and oxygenated blood flow. Some signs that your veterinarian would recognise would be abnormal sounds within the dog’s lungs, an enlarged liver and a heart murmur.

Overall, the FDA classifies this disease into 4 stages:

  • 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 class 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 whereby blood flowing back to the heart is physically blocked by a large mass of worms. 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 die. 

Treating Heartworm

There are a few FDA approved treatments available for dogs that could be prescribed by your vet such as:

  • Melarsomine dihydrochloride (available under the trade names Immiticide and Diroban), an arsenic-containing drug that is FDA-approved to kill adult heartworms in dogs. It’s given by deep injection into the back muscles to treat dogs with stabilized class 1, 2, and 3 heartworm disease.
  • Advantage Multi for Dogs (imidacloprid and moxidectin), an FDA-approved topical solution to get rid of microfilariae in the dog’s bloodstream.

However, treatment for heartworm disease could be potentially toxic to our doggo’s body, causing serious complications such as life-threatening blood clots to their lungs. Plus, it would require multiple visits to the veterinarian, blood tests, x-rays, hospitalisation and a series of injections which could be painful and harmful to our wallets.

Prevention Is Better Than Cure

Monthly administered preventives that are prescribed by your vet would be the most effective method. It would also mean having your doggo regularly tested to ensure they’re heartworm-free to begin with.

Plus, as a mosquito borne disease, we can also adapt some methods of dengue prevention practices such as:

  • Using screens in open doors and windows to prevent mosquitoes from entering our homes
  • Getting rid of standing water indoors and outdoors so these mosquitoes would not have breeding grounds
  • Using dog-friendly bug sprays or natural herbs such as lemongrass
  • Keeping our homes cool and dry so the mosquitos would not have a hot and humid environment to make themselves at home


Like all health issues, staying vigilant and actively preventing it from happening is key to ensuring our doggo’s longer life and happiness.

Besides a healthy diet and lifestyle, always remember to bring your doggo for their regular check ups and check in with your vet should you notice that something’s amiss.

Share this article with a friend:

Try a Petchef Meal Plan!

At Petchef, we believe in giving your furkids the very best. We use 100% fresh, natural ingredients that will benefit their health! Just a few easy steps to kickstart their healthy diets:

  • Tell us your pet's details

  • Choose their favourite recipes

  • We'll calculate a monthly plan for you

  • Then we customise and cook nutritious meals

  • And finally we deliver it to your doorstep

Related stories