dog sleeping under blanketHeartworm symptoms in dogs are subtle to begin with and can take some time to appear. Heartworms can be very dangerous and deadly, and they should be treated as soon as possible.

Heartworms are preventable in dogs! Talk to your veterinarian about putting your puppy or dog on heartworm prevention if they are not already taking one. Preventing the disease to begin with is much better than treating the disease.

What are Heartworms?

Heartworms are worms that enter a dog’s blood stream in the form of larvae as they enter the blood stream through a bite and will mature into adults and reproduce.

How Do Dogs Get Heartworms?

Heartworms are spread when mosquitoes that carry infected heartworm larvae bite dogs. It will take about 6 months for the larvae to reach the heart and lungs. Adult heartworms can be 12 inches long and more, and they can reproduce directly into the dog’s blood stream.

Heartworm Symptoms

These symptoms can be signs of heartworms or another disease. If you notice any of the symptoms below, see your veterinarian.

Dry Cough

You may notice an occasional dry cough, not persistent.


Your dog is not as active or tires quickly, doesn’t want to go out or doesn’t want to play. Heartworms will cause fatigue and inactivity.

Weight Loss

You may notice a loss of weight in your dog due to a lack of appetite.

Rapid Breathing

Rapid or labored breathing, along with coughing, occurs when the heartworms enter the lungs and surrounding veins.

Bulging Chest

Fluid can buildup in the chest due to the heartworms presence.

Allergic Reaction

Some dogs will show symptoms similar to allergic reactions or asthma.


If your dog collapses, rush them to the veterinarian hospital immediately.

Bernese Mountain dog laying downHeartworm Stages

Stage 1

Stage 1 for heartworm disease in a dog can mean there are no visible symptoms or minimal signs which could be an occasional cough. At this stage, a blood test may come back negative.

Stage 2

Heartworm disease at stage 2 will have moderate symptoms that can include coughing and inactivity. You should be able to detect the symptoms at this stage with a cough and fatigue.

Stage 3

Symptoms of stage 3 heartworm disease may be a persistent cough, inactivity and difficulty breathing. The disease can be seen on x-rays at this stage.

Stage 4

Dogs with stage 4 heartworm disease will have a persistent cough, severe fatigue and difficulty breathing. Some dogs at this stage may faint or have cardiac arrest.

Test For Heartworms

A blood test can detect heartworms, along with other abnormalities and to evaluate organ functions. If heartworms are detected, other tests will be run to evaluate your dog’s health.

Treatments For Heartworms

There are treatments that can cure most dogs from heartworms. The first round of treatments will target the adult worms and will take about one month.

The next treatment is to target the younger worms and offspring. After the worms are eliminated, they are absorbed by the body. In extreme cases, surgery may be necessary.

Heartworm Prevention

Heartworms are preventable! Let me say that again, Heartworms are preventable! There are preventative medications to prevent heartworms in dogs. If your dog or puppy is not on a heartworm preventative, see your veterinarian as soon as possible. This horrible disease is preventable!

For more information about heartworms from PetMD, click here. Leave a comment below or share a story about your dog or puppy. The information on this website is not intended to replace the advice of your own veterinarian, dog trainer, or dog behavioral specialist.