Wiki Toolbox

Dog Heartworms

From Pet Health Learning Center

Jump to: navigation, search


Heartworms are parasites that can cause harm to a dog by living inside of their heart and large blood vessels. Along with dogs, heartworms can also be found in other domesticated pets, such as cats and ferrets. They can also occur in wild animals, such as sea lions, foxes, and wolves, for example. Although it is extremely rare, heartworms have also been found in humans.

These parasites were first discovered in 1847. The most frequent cases were primarily found in the southeastern part of the United Sates. In recent years, the parasite has been found in dogs and other animals nationwide.


An infested dog will carry heartworms that will lay larvae that live in the bloodstream. Then, the larvae will be sucked into a mosquito when it feeds from a dog and live inside of the mosquito for 2 to 3 weeks. Once they mature, they will migrate towards the mosquito's mouth and enter the bloodstream of another dog when the mosquito feeds again from the mouth.

Once the larvae are inside the body, they will grow and start their migration towards the heart. Inside of the heart, they will grow into adults that can reach up to 14 inches long. From there, it can take about 6 to 7 seven months for the heartworms to lay new larvae and start the process over again.

Adult heartworms can live inside of a dog's heart for about 5-7 seven years, and a dog that is severely infested can have up to a few hundred heartworms living within its body.

German Shepherd Dog heart infested with heartworm. The heart is in a jar filled with formaldehyde. The orientation of the heart is sideways, with the apex to the left, and the great vessels to the right. The right ventricle is cut open, allowing the heartworms to be seen at the bottom.


While living inside of the heart and blood vessels of a dog, heartworms can obstruct the vessels that connect the heart to the lungs. A dog's heartworm condition is known as severe when the parasites start obstructing the right ventricle of the heart.

Symptoms and Diagnosis

Usually, dogs that are infested with heartworms never show any signs of the disease. But, some common, yet subtle, indicators include: decreased appetite, weight loss, and listlessness. Respiratory problems are also another sign of the disease. Infected dogs may cough or exhibit a lack of endurance during exercise. In very rare cases, a dog that is infested may suddenly die of heart failure due to the heartworms.

To determine if a dog has Dog Heart Disease caused by heartworms, a blood test is performed that is accompanied by an examination of symptoms and history. To confirm, an ultrasound or an x-ray may be needed to view any changes within the heart or lungs that are typically caused by heartworms.


One of the first treatments for heartworms was adulticide, which contained arsenic. This drug was used to kill the adult heartworms by intravenously distributing the drug. But, this drug caused many health issues, so it's no longer used to treat heartworms in dogs.

Other medications of the same sort of adulticide are often used, but they are entered through a dog’s muscles and are far less likely to cause any further damage.

The protocol of treatment depends on the severity of the infection, so each dog's treatment will be different.


Regardless of the treatment, once the parasites die, they can further obstruct the heart and blood vessels. So, the best way to protect a dog from heartworms is to prevent them entirely with a prevention program that includes regular checkups and medications.

Ask an Expert


Dr. Janice Huntingford

Doctor of Veterinary Medicine

Customer Service

1 877 633-2401

Live chat by BoldChat

Click to verify BBB accreditation and to see a BBB report.

90 day money back guarantee