top of page


If you have a dog or cat, you’ve probably heard a lot about heartworm disease, as us veterinarians like to spend a lot of time talking about it. Heartworms, as you might imagine from the clever nomenclature, are worms that live in the blood vessels of the lungs and the heart of your furry friends. This is a problem because what is suppose to be in the heart and vessels is blood; a foot-long worm tends to obstruct and disrupt the blood flow. (This can result in lots of problems, including heart failure, coughing, pneumonia, nose bleeds and/or sudden death.)

How Did A Foot-Long Worm Get Into My Pet?

So how do these big ol’ worms end up there? Let’s follow the circle of life! Like just about every other living thing, a heartworm’s main objective in life is not to kill dogs but to reproduce. Yes, they’re not only hanging out, dancing around in the heart and lungs and generally wreaking havoc, they are actually breeding in there. They produce cute little micro-baby heartworms called microfilariae, which hang out in the bloodstream, just waiting for a mosquito to land on the poor, unsuspecting doggy host for a quick meal. The mosquito bites the dog and, just like an alien abduction, the microfilariae get sucked up into the mosquito-shaped UFO and away they go.

They spend their childhood in this mosquito, where they learn all about swimming and navigation, which will come in useful when it’s time to find a heart. One day, when they are mostly grown up, the mosquito bites a new host dog or cat and they are spit out, swimming under the skin where they finish up their education. Finally they are ready to enter the mammal’s bloodstream, where they travel to the heart and lungs, get big and yes, we are back to reproducing. (Well, only in dogs; in cats, the worms are kind of confused and just swim around, making kitty very sick or dead.)

That sounds awful, doesn’t it? We don’t want this happening to beloved Fido or Fluffy. That’s why your veterinarian keeps recommending heartworm prevention. There are several different kinds of heartworm preventatives; most of them have an added bonus of doing even more then kicking baby heartworm butts! Sadly, none of the preventatives kill the adult heartworms.

We will discuss the added bonus of preventative measures in the next post; but what happens if your best canine friend has mature heartworms? What can you do?

Treatment Options:

There are several treatment options for dogs and one for cats with adult worms and to be perfectly honest, I would say none of them are good.

For dogs, one option is surgical removal. If you’re never planning on eating again, here’s a video you can watch of the surgical removal of some adult heartworms: HERE

Another canine option, probably preferable to surgery but also unpleasant, is a drug called Immiticide. This is a very painful drug that goes deep into muscle; it is given 2-3 times to kill adult heartworms. After each injection, the dog gets to sit in a cage for a month to minimize side effects, which is okay because his butt will probably be sore for that whole month from the injection. This will probably not be the most fun time in your dog’s life. The other downside of Immiticide is that it is not always available.

The final option for dogs is a medication called Ivermectin. This medication is found in some preventatives; it actually is not able to kill the adult heartworms, so it’s a little deceptive for me to put it in the option category at all. It is the “doing nothing” option. If you keep giving it, it will keep killing the babies and eventually the adults should die by themselves after a couple years.

In cats, if you can believe it, the treatment options are even bleaker. Immiticide is so potent that it will actually kill your cat, so that option is usually off the table. If I treat a heartworm-positive cat, I start her on steroids (This does nothing to kill the worms, but it does suppress her own immune system so that her symptoms are lessened) for a couple of years and wait and wait and wait for those worms to die, hoping that they don’t kill the kitty in the meantime. Steroids themselves have a lot of side effects too, so for many reasons this is not ideal.

The good news is that heartworm disease is 100% preventable by using those products that we veterinarians keep talking about. So use them!

Featured Posts
Recent Posts
Search By Tags
Follow Us
  • Facebook Basic Square
  • Twitter Basic Square
  • Google+ Basic Square
bottom of page