Valentine’s day is right around the corner.  I bet when you think of  LOVE you are not thinking about HEARTWORM.  Veterinarians, they are thinking about HEARTWORM!  

For “Ask The Vet,” Dr. O’Hara and I talk about heartworm and how serious it is. To be honest I had no idea how dangerous heartworm is for our dogs and cats. Left untreated it can lead to serious health complications and sadly it can often be fatal. Heartworm is a big deal. With that said, heartworm is preventable and in many cases if it is caught early it is treatable.

This is Chewie and he had heartworm. Chewie was adopted by Dr. O’Hara and unfortunately he tested positive for heartworm.   Watch this VIDEO of Dr. O’Hara and Chewie to learn about prevention and treatment.  You will also find out how Chewie is doing today.



Heartworm is easy to get and difficult to treat. It can be a potentially fatal disease that is transmitted by mosquitoes to dogs and cats. Heartworms, also known as Dirofilaria immitis, spend their adult life in blood vessels connecting the heart and lungs and in more advanced cases inside the heart.

A diagram of the cycle of Heartworm.

  • Adult heartworms lay very tiny larvae called microfilariae, which travel throughout the bloodstream. 
  • When a mosquito sucks blood from an infected animal and bites its next victim the larvae are transmitted through the skin.
  • The larvae make their way to the chambers of the heart or lungs where they grow into adults.
  • They can grow up to 10–12 inches in length.

The symptoms

DOGS:  Symptoms can vary in dogs but most commonly include: breathing difficulties, coughing, reduced appetite, and weight loss and lethargy.

CATS: Symptoms in cats can include vomiting, gagging, difficulty or rapid breathing, lethargy and weight loss. Signs can often be mistaken for feline asthma or allergic bronchitis.

My pet tested positive for Heartworm. Now, what?
It can be complicated and expensive to treat heartworm for your dog. Your pup will have to go through a series of treatments over the course of a few months.  Adult heartworms in dogs are killed using a drug called adulticide that is injected into the muscle. Treatment may be administered on an outpatient basis, but hospitalization is often necessary. 

Your pup will be restricted to limited exercise. Only leash walking. This is because you have to reduce the blood flowing through the lungs as the lungs can become blocked by dead worms. Preventive medications are also given to avoid heartworm reinfection and to eliminate any larvae that may be present.

For cats as far as I have learned there are no products in the United States approved for the treatment of heartworm infection. So disease prevention is critical with cats.


Prevention is the name of the game. Preventive therapy is safe, easy and inexpensive and is extremely effective. Ask your vet about preventive medications. It is recommended that heartworm medication be given year-round. If you do not want to give the medication over the winter treatment should be started one month before the mosquito season and continue for one month beyond the first frost.



Good boy Chewie!

Dog Prevention. 

  • Prevention should start at 6 to 8 weeks of age.  
  • Adult dogs are tested before being started on a heartworm preventive for the first time. 
  • All dogs should be tested annually. 
  • The test should be repeated annually.

Cat Prevention.

  • Preventives should start before the kitten reaches 9 weeks of age.
  • Cats over 6 months old should be tested for heartworms prior to starting prevention.,
  • All cats should be tested annually.

Preventives are worth every dollar spent!  They keep your pets safe. 

More information about prevention and treatment. If you think your pet has Heartworm contact your vet as soon as possible. Do not wait.

American Heartworm Society

WebMD: Healthy Pets

Tufts Cummings School of Veterinary medicine)