Symptoms of Heartworms in Dogs

Most dog owners have heard of heartworms but don't know the full story. When it comes to identifying if a pet has heartworms, this stealthy killer can be very difficult to pick up on until it's almost too late. In some cases, a pet owner doesn't realize their dog has been infected until a routine vet visit, but there are a few signs of heartworms in dogs that are noticeable.

What are heartworms?

Heartworms are long, noodle-like worms that live and grow in your dog's heart and lungs. They are transmitted by mosquito bites. When mosquitoes bite an infected animal (dog, fox, or coyote), they pick up baby heartworms in the blood that can be transmitted to your dog.

The baby heartworms migrate and grow over several months until they reach their final destination, the heart and lungs. From there, they will grow into foot-long adults, breed with other worms, and inflict serious damage.

How do you know if your dog has heartworms?

Dogs tend to show symptoms as the heartworms mature, which means that when you do find out that your dog has heartworms, it's probably already serious. Many people find out by having their vet perform a blood test, but there are a few physical signs of heartworms that dog owners can observe:

Cough. One of the most noticeable symptoms of heartworms is a cough. You may hear your dog coughing from time to time, especially after exercise. This can also indicate kennel cough, which is like bronchitis for dogs. Either way, a visit to the veterinarian is in order.

Lethargy or inactivity. Anytime there is a change in your dog's activity level or stamina, take them to the vet. Because heartworms get into your dog's heart, it can be difficult for your pet to complete even the easiest of activities.

Decreased appetite resulting in weight loss. As the heartworms mature and migrate into the dog's heart and lungs, the dog may lose their appetite. Losing weight may be a symptom of heartworm disease.​

Heart failure. In most cases, a veterinarian is going to recognize these signs more than a pet owner, but when the disease has progressed, the dog may have a heart murmur, erratic heartbeats, and your dog's stomach may get bigger because its abdomen is filling up with fluid.

Other signs. Some dogs will have blood in their urine and may even collapse because their hearts are almost completely blocked by the worms.

What to do if your dog has heartworms?

Your veterinarian will administer a series of treatments over the course of several months and you'll have to keep your dog calm and limit activity while the worms die off.

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