What Happens If You Miss a Heartworm Dose?
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Forgot a heartworm dose? Don't panic — but do act. Here's exactly what to do and why timing matters.
Why timing matters
Heartworm preventives work retroactively, clearing larvae your dog picked up in the previous weeks. Given on schedule, they stay ahead of the parasite. A missed dose can leave a gap where larvae mature beyond the preventive's reach.
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What to do first
If you're only a few days late, give the dose right away and resume the normal schedule. If it's been more than a couple of weeks — or you're unsure — call your vet before giving the next dose.
When a retest is needed
If you've missed doses for two months or more, your vet will likely recommend a heartworm test before resuming, and another test a few months later, since infection takes time to show up. This keeps your dog safe.
Prevent future lapses
Set a recurring monthly reminder, anchor the dose to a memorable date, or ask about longer-acting options. Consistency is everything. Our [free pet savings card](/card) can help keep prevention affordable so it's easier to stay on track.
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Frequently asked
- What should I do if I miss my dog's heartworm dose?
- If only a few days late, give it right away and resume the schedule. If it's been over two weeks, call your vet before the next dose — a retest may be needed.
- Is one missed heartworm dose dangerous?
- A single slightly late dose is usually low-risk if you catch up quickly. Longer gaps raise the risk of infection, so consult your vet if you've missed multiple doses.