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Jul 28 2016

Why does my pet need a heartworm test to get more prevention?

You bring your pet in for his wellness exam and vaccines.  You get your pet tested for heartworms and pick up a 6-month supply of preventative.  You promise to be diligent and give the dose every month.  Before long, you realize the box is empty and you call to get more only to be told you need a heartworm test.  Sure, maybe you missed a dose or two, but what’s the big deal?

First, it’s important to note that heartworm prevention does not last 30 days.  It is a dewormer that is in and out of your pet’s system in a matter of hours.  So you buy your prevention and start it at the 1st of the month.  Then, a few days later, your pet is bitten by a mosquito carrying heartworm larvae.  If you give your pet his preventative on the 1st of next month, it will kill that larvae and you will have no problems.

But what if you miss that dose on the 1st of the following month?  If you give it within a few days, you are still okay.  But once you get into the zone of being 45-65 days since the last dose, those larvae are large enough that your heartworm prevention may not kill them.  Five or 6 months later, larvae will be adult heartworms that will start to make their home in your dog’s heart and start having babies of their own.

Most heartworm preventatives only kill the larvae, so if you continue to give the prevention, all the new baby heartworms will die.  However, some preventatives have been known to kill adults as well.  Quickly killing adult heartworms can be fatal to your pet.  This is why it is recommended that you test for heartworms annually, if you have slipped on your compliance in the past,  if you have missed a couple of doses, or if your pet has been off of prevention for at least 2 months.

Keeping your pet on year-round prevention is best for your pet.  If you are having a tough time remembering to give your pet his heartworm prevention, call any of our staff at 898-8433 for some great tips.  And remember, when we require your pet to have a heartworm test, it is in the best interest of your pet.

For more information on heartworms, visit the American Heartworm Society at

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