PetFitness Blog – Pet Exercise, Workouts & Fitness Tips for Dogs

Heartworm Symptoms in Dogs

healthy dog

Heartworm illness causes long-term damage to the heart, lungs, and arteries, affecting the dog’s health and quality of life even after the parasites have been removed. In this article, we’ll dive into the different heartworm symptoms in dogs!

Heartworm Symptoms in Dogs

Heartworm illness is classified into four phases. The worse the sickness and the more visible the symptoms, the higher the class.

Left untreated, heartworm infestation in dogs can lead to a whole variety of symptoms.


Anemia refers to a decrease in red blood cells, which can cause loss of energy and stamina, pale gums, and cold limbs.


Lethargy and aversion to exercise are frequent symptoms of severe heartworm illness in dogs.

If your pet loses interest in going for walks or becomes tired after exercise, this might be an indication of heartworm disease.

Speaking of which, if your dog doesn’t have a heartworm preventative yet and you’re scared to take them out for a walk, you can use a treadmill in the meantime.

Weight Loss and Appetite Loss

A dog with heartworm disease is often too weak to consume enough food, even if it has a strong appetite.

If you notice your dog suddenly losing weight or losing interest in eating, make sure to schedule an appointment with their veterinarian. Your vet can rule out any other illnesses and confirm if they are suffering from heartworms.

Persistent Cough

Coughing is another symptom of heartworm illness in dogs. In fact, persistent coughing is a sign that the heartworms have reached the lungs and surrounding arteries.

This is often a dry, ineffective cough that becomes more noticeable after activity. That said, coughing is also a common symptom of other canine ailments, so it’s important to schedule an appointment

Frequent Allergies

While cats are more likely to have an allergic response to heartworm infection, dogs can also develop asthmatic-like symptoms that mimic allergies.

Frequent sneezing, wheezing, and other signs of respiratory distress can indicate heartworm infection.

Seizures or Blindness

Heartworms can spread beyond the heart and into the brain and eyes, where they can cause convulsions and blindness. Although these symptoms are uncommon in heartworm illness, they should be taken into account.

Swollen Stomach

As heartworm disease progresses, you may notice a bloated abdomen as fluid accumulates in the stomach. This is one of the more serious heartworm symptoms in dogs and should be addressed immediately.


Heartworms can obstruct blood flow, particularly in the vena cava, which is the blood vessel responsible for bringing blood to and from the heart. Known as vena cava syndrome or caval syndrome (CS), it occurs when heartworms clog the right atrium, right ventricle, and of course, the vena cava.

In this situation, dogs may faint due to insufficient blood supply reaching its brain and may even go into shock. By now, the illness has progressed so far that survival is highly unlikely.


Heartworm disease is a serious and potentially deadly illness for dogs. If you notice any of these heartworm symptoms in dogs, visit the vet as soon as possible.

Also, heartworm preventatives are available for both cats and dogs. These can help reduce the chance of your pet contracting heartworms in the first place.

For more information on dog health and disease prevention, make sure to check out our blog at PetFitness!

Join Our Pack

Subscribe to our blog for more free tips and techniques to keep your dog fit, as well as discount codes for exciting doggy products.

    Follow Us On Social Media

    Related Posts