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I accidentally missed my dog's Heartgard. What now for heartworms?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed | Female | spayed

I might have accidentally skipped Heartgard for 1 month. Not positive, but the following month when I went to give it, the pre-written month on the package didn't match and made me think I might have forgotten (unless I just randomly grabbed one the month before). I read that a blood test won't detective heartworms until 6 months later. My dog's annual is around then. Should I wait until then and see, or is there something I should do sooner?

2 Answers

Most Helpful Answer

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Answered By Destini R. Holloway, DVM

Veterinarian

Published on December 17th, 2018

If you only missed 1 month, you should be fine. Just resume Heartgard right away . If you just want peace of mind, then you can have Lilly retested in 6 month from now; however, the chances of infection are pretty low. Thanks for visiting Petco Pet Education Center, formerly Petcoach and best wishes with your pet Lilly. Take care!

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    Answered By Sara Farmer, DVM

    Veterinarian

    Published on November 6th, 2019

    If it has been 6 months or more since the missed dose it is best to re-test for Heartworm before starting preventative. If it has been less than 6 months it’s okay to go ahead and start the medication. It takes 6 months for heartworms to mature and the test only looks for adult heartworms, so even if a dog has been infected with heartworms the test will be negative for the first 6 months.

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