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My puppy missed heartworm medicine. Should I worry about heartworms?

Updated On September 23rd, 2025

I was given heartworm medicine for my puppy at 9 weeks old and forgot to give it until 12 weeks. Should I be worried about heartworms.

2 Answers

Most Helpful Answer

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Answered By Lauren Jones VMD

Veterinarian

Published on June 28th, 2022

Anytime heartworm prevention is late or missed, there is a chance of acquiring heartworm disease. Given your southern zip code, you're in an area of a much higher incidence of heartworm disease relative to those of us further north. With that said, I don't think you need to panic! Since your puppy is still so young, they're too young to run a terribly accurate test for the presence of heartworms. The tests that we use as a screening tool check for the antigen from adult female heartworms, which take at least 5-6 months post infection to show up on a test. My point being, I think it's worth asking your vet to run a heartworm test on your pup in another 6 months. In the meantime, certainly continue giving the heartworm preventive medication consistently every month. Remember that as your puppy grows, their dose will change, so keep in touch with your vet regarding your puppy's current weight and dosage. I hope this helps to clear up any confusion and that everything goes well for your pup!

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    Answered By Dr. Melanie, BVSc MS

    Veterinarian

    Published on

    Not to worry, typically heartworm medicine should be given once a month (every four weeks, so if you gave it at 9 weeks, it was next due at 13 weeks. Read the directions on the package for the instructions on how to give it. I hope this helps.

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