PetMed Animal Health Center

2400 Gateway Dive
Dubuque, IA 52003


Heartworm Disease & Prevention

What It Is: Heartworm Disease is a very serious and even fatal disease in pets. It is caused by foot-long worms that grow and live in the heart, lungs, and blood vessels of the pet. 

Transmission: This disease is essentially transmitted by mosquitoes. When a mosquito bites an infected animal and feeds on the blood, it is picking up the microscopic baby worms called microfilaria that are produced by the female heartworms. The microfilaria circulate the bloodstream which makes it so easy for the mosquito to transmit. For about 10-14 days, the microfilaria develop into the larvae or otherwise known as the "infective stage". Once this stage is reached, they are able to infect the new host or pet once the mosquito bites into it. When the mosquito bites into another dog or cat, the larvae enter through the bite wound and infect the new host. 

Health Concerns: There are several great health concerns with this disease as it can be essentially fatal. These heartworms can cause severe lung disease, heart failure, and damage to other organs in the body. 

Who Is At Risk: Dogs- Dogs are a very natural host for heartworms because they are able to mature into adults, mate, and reproduce. When left untreated, the number of heartworms in a dog can increase to several hundreds of worms in their body. This disease causes extensive damage to the heart, lungs, and arteries causing the quality of life of the dog to decrease dramatically even after the worms have gone after treatment. This makes dogs the most at-risk over cats, etc. 

Cats- Heartworm disease in cats is quite different than dogs. Cats are not a general host for the heartworms being that most worms in cats do not survive maturing to adults. That being said, if a worm happens to make it to the adult stage, it is usually one to three that live. 


A regular monthly heartworm prevention and yearly testing is the best way to ensure that your pet does not contract this disease. PetMed Animal Health Center supplies Tri-Heart Plus as well as the tests. The prevention is based on weight being there are three different weight classes. Prevention can be started in puppies as young as 6 weeks of age as well as pregnant female dogs. It is best the continue the prevention year round because missing one dose or stopping the prevention for winter months puts your dog at risk. Mosquitoes are adapting to new climates everyday and are also able to thrive in homes and buildings in the colder months. Yearly testing is highly recommended because just like people, animals can become resistant to medication.