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Heartworm Disease Prevention

Updated: Apr 9

What is Heartworm Disease? How does my pet contract it?

Heartworm disease ia serious and potentially fatal disease in pets. Heartworms are parasitic worms that are transmitted to dogs by infected mosquitoes. When an infected mosquito bites your dog, the mosquito can also pass on infective larvae. These microscopic larvae develop under the skin, and then migrate to the blood vessels of the heart and lungs of the infected animal where they rapidly grow damaging the lungs and heart

They can clog vessels and interfere with blood flow. Heartworm disease can affect the dog’s health and quality of life long after the parasites are gone.  Left untreated, heartworm disease can cause heart failure and even death.


Some dogs don’t show any signs of infection. Other dogs can develop severe signs like:

  • Coughing

  • Difficulty Breathing

  • Lethargy

  • Swollen Belly


Heartgard Plus (or some other Heartworm Preventative) is given to dogs every 30 days as a monthly heartworm preventative and can effectively kill any Heartworm larva that may have been injected by a mosquito. Clients often report that they have forgotten to give a dose (or two or three) during the preceding six months or year. This reduces the effectiveness of the preventative treatment.

Heartgard Plus chews prevent heartworm disease and can also treat/control 5 species of intestinal worms simultaneously (3 species of hookworms and 2 species of roundworms). Hookworms and roundworms pose a serious threat to dogs. Left untreated, they can cause blood loss, weight loss, and/or diarrhea. While uncommon, in more serious cases, they can even cause death.

American Heartworm Society recommends that heartworm disease prevention for puppies starts no later than 8 weeks of age.

Prior to starting prevention, and annually after giving Heartgard, we require heartworm testing to make sure that the pet is still free of this parasite annually.

There are two basic tests we perform to detect Heartworm disease in dogs. The first test is submitted to a commercial laboratory and the results are usually received the next day. The second method of testing for Heartworm disease is done with an “in-house test” that can be done while you wait for the results (30 minute wait)

But what if clients forget the monthly Heartgard Plus dose often?

ProHeart Injections is an alternative that is gaining popularity for prevention of Heartworm disease:ProHeart6 and ProHeart12. These are single injections that are administered by our professional staff once every six or twelve months. It takes the worry out of remembering when to give the monthly chewable medicine. When you come to our clinic for your annual Heartworm test, we will discuss this option with you. If you are happy with the monthly chewable medication, there is no need to change. But if you are interested in making sure your pet never misses a dose of heartworm prevention in the future, you may want to consider ProHeart6 or ProHeart12.

Why do I need to test if my dog has been on Heartworm prevention?

An understanding of the method of transmission and treatment for heartworm disease is needed. When a pet takes Heartgard, a couple of the larval stages of heartworm disease are treated. This is a time-sensitive process. If Heartgard is given too late, and if an infected mosquito bites your pet at just the right time, the medicine will not be effective in preventing a full-blown infection. The current recommendations of the American Heartworm Society are that pets be tested annually. We recognize their guidelines as the most authoritative in our profession. In addition, if a pet ever does develop Heartworm disease and the client has been following our protocol faithfully (monthly dosing and annual testing), the cost of treatment for the infection is primarily borne by Merial, the manufacturer of Heartgard and Frontline. Even though this is unlikely, it gives us peace of mind that they stand behind us and your pet.

Here are some helpful links to learn more!


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