Cat with Yorkshire

Heartworm in Dogs and Cats

Heartworm is a potentially devastating disease that can occur in both dogs and cats. It can be difficult to diagnose until it's in advanced stages, which means screening and prevention is vital for protecting your pets from Heartworm.


Heartworm is caused by the parasite dirofilaria immitus, and it's carried from host to host by infected mosquitoes. Heartworm cannot be transmitted through direct contact. When an infected mosquito bites your pet and injects the heartworm larvae, the larvae travel through the bloodstream and become lodged in the heart and blood vessels. As they grow into adults, the larvae cause inflammation and impede blood flow, causing severe damage to the heart and other organs. This usually leads to death.


Even though heartworms can grow to be 6-14" long, the symptoms aren't noticed until months to years after the initial infection. Dogs may have a soft cough, difficulty breathing, weakness, fainting or weight loss. Cats may also experience vomiting or gagging. If not treated, the animal usually dies of heart failure.


Treatment includes eliminating all forms of the parasite—adult, larvae and microfilaria (prelarval stage). Multiple injections are often used to kill the adult heartworms, and antibiotics to prevent secondary pneumonia. After treatment kills the adult heartworms, a Heartworm preventive is often used to kill the microfilaria.

The animal must be closely monitored with restricted activity for six weeks after treatment while the dying heartworms are removed from the blood stream. Restricted activity is to prevent the dying worms from breaking off in pieces that could plug the arteries of the lungs. Heartworm treatment is tricky depending on the level of infestation; it may be difficult to prevent more harm than good. Currently there is no approved treatment for Heartworm in cats, so only the symptoms can be treated.


Treatment is expensive and difficult, so prevention is key to managing heartworms. There are a variety of safe monthly preventatives available with a veterinarian's prescription, including Heartgard® and Iverhart®. Most Heartworm preventatives work by killing the immature larvae, which prevents them from maturing into adults. Before prevention is started, your pet should be blood tested to be sure he is free of existing Heartworm. Your pet should also be periodically re-tested.

Your pet’s monthly Heartworm prevention is important in keeping them healthy!

If you need help, call us at 1-800-786-4751.

-The Revival Education Team

The materials, information and answers provided through this website are not intended to replace the medical advice or services of a qualified veterinarian or other pet health care professional. Consult your own veterinarian for answers to specific medical questions, including diagnosis, treatment, therapy or medical attention.

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