Common Symptoms Of Heartworm In Dogs

They’re not fun 😨

dog heartworm symptoms

Heartworm in dogs is no joke.

Heartworm testing should be a part of your dog’s annual wellness exam, but what if your dog gets heartworm during the time between tests?

Sometimes, you’ll be able to tell your dog has heartworm if he displays one or more of the telltale signs (which means get him to the vet ASAP). 

The Dodo spoke with Dr. Zach Marteney, a veterinarian and medical director at Meadowlands Veterinary Hospital in New Jersey, and Dr. Claire Walther, the parasiticides medical affairs lead at Zoetis Petcare, to learn all about common symptoms of heartworm in dogs — so you’ll know what things to watch out for.

What is heartworm in dogs, anyway?

Basically, heartworm is exactly what it sounds like — a worm in your dog’s heart.

Obviously, anything foreign inside your pup’s heart poses a huge problem, since it can cause some serious issues.

“This is a parasitic infection where worms damage all aspects of the heart,” Dr. Walther told The Dodo.

That damage can be caused by the heartworm itself or your dog’s immune response to it (or both).

“Heartworms move with the blood flow through the pulmonary artery, causing both physical damage to the inside of the vessel, as well as inflammation as the dog’s immune system senses the invaders and tries (unsuccessfully) to clear the worms,” Dr. Marteney told The Dodo.

Symptoms of heartworm in dogs

While some dogs will show symptoms, one of the scariest things about heartworm in dogs is that most of the time, there aren’t any visible symptoms at all.

“Some dogs do not have any clinical signs with heartworm disease,” Dr. Marteney said. “They have a subclinical infection that is only identified on their routine annual heartworm test.”

That’s why regular screenings are so important.

If your dog does show symptoms of heartworm disease, there are a few things you should look out for.

Mild symptoms

Some mild heartworm symptoms in dogs include things like:

  • Coughing
  • Decreased energy level
  • Running out of breath quickly while exercising

Severe symptoms you can see

Those heartworm symptoms can get even more intense if your dog’s heartworm disease has become severe.

Symptoms of serious cases of heartworm in dogs include:

  • Significant coughing
  • Coughing up blood
  • Significantly increased respiratory rate
  • Difficulty breathing
  • Decreased overall energy level
  • Abdominal swelling

The reason abdominal swelling is listed as a more severe symptom is because it could be a sign that something incredibly serious is going on.

“Abdominal swelling can be a sign of severe late-stage disease,” Dr. Marteney said. “This fluid accumulation is a sign of right-sided heart failure.”

Severe symptoms you can’t really see

What’s even scarier is that there are serious heartworm symptoms in dogs that occur internally, so you won’t be able to see that they’re happening.

Some internal heartworm symptoms include:

  • Internal inflammation
  • Increased blood pressure
  • Heart failure
  • Liver damage
  • Kidney damage
  • Blood clots

A lot of these symptoms can occur because heartworm causes internal inflammation as your dog’s body tries to fight off the parasite on its own.

“The inflammation causes the artery to harden, increasing the pressure in the vessel and forcing the right side of the heart to work harder,” Dr. Marteney said.

This added pressure can cause other problems, like heart failure.

“As it works harder, the heart enlarges and can eventually fail to pump blood to the lungs effectively,” Dr. Marteney said. “Right-sided heart failure can cause accumulation of fluid in the abdomen and damage to the liver from blood backing up in the vessels inside that organ.”

And heart failure isn’t the only serious, life-threatening condition that heartworms can cause. Your dog’s kidneys are also at risk. 

“Kidney damage can also result from heartworm disease as a result of the body’s immune response to the worms,” Dr. Marteney said.

Blood clots can also occur.

“You also have the risk of what happens when that worm dies,” Dr. Walther said. “That worm can also cause blood clots, for example.”

How do dogs get heartworm in the first place?

Dogs get heartworm through mosquito bites.

“A dog has to be bitten by an infected mosquito in order to get heartworm disease,” Dr. Walther said.

Mosquitos bite an infected dog, and the heartworm larvae mature inside it.

The heartworm will make its way through your pup’s tissue and ultimately get to his heart, where it’ll live within the pulmonary artery.

Heartworm prevention for dogs

The best way to keep your dog from experiencing heartworm symptoms is to prevent heartworm altogether with a prescribed medication.

“What heartworm preventative does is it removes that larval stage before it can grow up to be that scary, foot-long, damaging worm,” Dr. Walther said.

There are a couple different types of heartworm prevention for dogs, from monthly medications to annual injections to combination tablets that are also effective against fleas, ticks and intestinal worms.

Heartgard Plus is a highly-rated chewable tablet designed to prevent heartworm in dogs. It’s available for dogs up to 25 pounds, dogs 26 to 50 pounds and dogs 51 to 100 pounds.

As far as combination medicine goes, Simparica Trio works to prevent heartworm, fleas and ticks. It’s available for dogs 2.8 to 5.5 pounds, dogs 5.6 to 11 pounds, dogs 11.1 to 22 pounds, dogs 22.1 to 44 pounds, dogs 44.1 to 88 pounds and dogs 88.1 to 132 pounds.

You need to have a prescription for these, so a chat with your vet should help you figure out which heartworm prevention option is right for your dog.

Heartworm treatment for dogs is available, but the best way to make sure your pup is happy and healthy is to prevent him from getting the disease entirely.

We independently pick all the products we recommend because we love them and think you will too. If you buy a product from a link on our site, we may earn a commission.