heartworms in dog

You've probably heard of heartworms. These parasites enter your pet's bloodstream through a mosquito bite, then grow up, infest their hearts, and do serious damage to their internal organs. The details are gross, but the more you know, the more power you have to help your pets avoid this serious health risk and stay alive and well.

What is a heartworm?

Heartworms, or Dirofilaria immitis, are small, threadlike worms that love to take up residence inside your pet’s pulmonary arteries (large blood vessels that run between the heart and lungs). If you have a strong stomach, you can look up images – but be warned, they may spoil dinner.

In dogs, heartworms can grow up to 12 inches long. Worse, there can be as many as 250 of them residing in an infected heart. This mass of worms poses a serious risk to your pet, causing everything from a harmful inflammatory reaction to blockages of blood flow, organ failure, and sudden death.

In short, heartworms are very bad news, and you do not want your pet to have them.

Who gets heartworms?

Heartworm infections are spread by mosquitoes. When mosquitoes feed from an infected animal host, they pick up tiny heartworm larvae, which they then pass along to the next animal they bite: dogs, cats, sea lions, wolves, coyotes, and foxes.

That’s right – unfortunately, both cats and dogs can get heartworm. And it doesn’t matter where you live. Heartworm is a risk for pets of every age, breed, and location, indoors and outdoors, all across the 50 states. 

What kills heartworms?

Heartworm is a disease that is definitely better to prevent than cure, especially because serious organ damage can occur before you even know your pet is infected.

Happily – and you knew we’d have some good news! – heartworm prevention is easy. You can choose from a wide range of heartworm prevention products, including topical solutions such as Revolution^® Plus for cats, oral medications like Simparica^® Trio for dogs, and even injections like ProHeart^® 6 or ProHeart^® 12 for dogs which last up to 6 or 12 months, respectively. Your Banfield Pet Hospital veterinary team will have all the information you need to find the right year-round prevention choice for you and your furry friend.

What if my pet already has heartworms?

Hosting parasites inside their ticker is a huge risk to your pet's good health. Definitely see your veterinary team for regular tests and wellness checkups. Signs of infection include a dry cough, rapid breathing, shortness of breath, lack of appetite, fatigue after moderate activity, and weight loss. As the disease progresses, severe symptoms include the appearance of a swollen belly and congestive heart failure.

If your dog's blood tests positive for heartworms, your team will recommend a multi-month course of treatment. First up is medication to kill developing heartworms, then medication to kill existing adult worms. Your pet will need to be closely monitored and their physical activity level severely limited, because any heartworm infection brings with it the risk of organ damage and even organ failure.

Remember, your absolute best strategy is stopping the disease from starting in the first place. A heartworm treatment regimen is currently only available for dogs; there is no approved treatment for the disease in cats, so preventive treatment is especially important for your feline friends.

Here’s another great way to earn more about heartworms.