3 Heartworm Prevention F.A.Q.s

What should you do if your dog misses a dose of heartworm prevention?

I Missed Giving a Dose of Heartworm Prevention Medicine. Does My Pet Need to Be Tested for Heartworms?

We’ve all been there at least once in which life’s daily routines can cause us to forget important reminders. So, what happens in the event you mistakenly forget to give your pet his or her heartworm preventative and a month goes by without protection?

Despite potential misinformation given to pet parents, it is not necessary to have a pet immediately tested for heartworms if a pet has missed one month of heartworm preventative medicine. The reason for this is because it can take several months for a pet to become heartworm-positive if he or she is bitten by mosquitoes carrying heartworms. Also, most of the monthly heartworm preventatives have a safety factor of at least 15 days of protection if a dose is missed.

When Should I Resume Heartworm Preventative After a Missed Dose?

The simplest answer to pet parents who forget a month of heartworm prevention is to simply give the pill or administer the application and restart their monthly preventative schedule. At the time of an annual or semiannual exam, a routine blood test is recommended, along with a wellness exam and other laboratory testing if necessary. While I encourage pet parents to maintain their monthly heartworm preventative scheduling, accidentally missing a dose will not be a health risk or harmful to one’s pets in these isolated circumstances.

Why Does My Dog Vomit After Taking Heartworm Preventative?

In some cases, pet parents may notice their pet experiencing a digestive upset after administering an oral heartworm preventative. For some pets, this may be a one-time only instance and I will advise pet parents to resume the monthly heartworm medication the following month. If vomiting occurs with subsequent administration, it is possible your pet may have an allergic reaction to the ingredient. As a result, consider changing to a different brand of monthly heartworm prevention, or consider topical preventatives such as Revolution or Advantage Multi.

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  1. i think it can be harmful to miss a dose……….

  2. The test of HW was positive for two of my dogs and I need two treatments. One of my dogs weights 58 lbs., and the another is 64 lbs.

  3. Dr. Michael Dym, VMD veterinarianApril 17, 2014 at 11:38 pm

    I would recommend seeing local vet for possible heartworm adulticide treatment with injectable drug called immiticide.

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  5. I have a for year old sweet Beagle/Rat Terrier Mix I adopted and he was HM + when I got him two years ago. These past 3 months have really taken a toll on me financially and was not able to get his Hartguard. Will he be okay? What can I do to ensure he will live for a long time? Thanks.

  6. Dr. Michael Dym, VMD veterinarianJune 29, 2014 at 4:25 pm

    I would just feed him an all natural diet like wysong epigen diet from 1800petmeds, as well as get him heartworm tested and back on heartworm prevention. Consider multi vitamin like vita chews from 1800petmeds, as well as antioxidant like proanthozone for long term health.

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  8. I have a question concerning Heartworm medication,and my dog vomiting. I normally feed my dog twice per day..Today it was time for my dog’s monthly Heartworm medication dose,so I gave my dog her Heartworm medication along with her first feeding at 1:30pm,and then her evening feeding later around 8:00pm.

    At 11:30pm she vomited while I had her outside.What happened when I took her outside was,is that I walked down the stairs of my deck into the yard,and turned around to see where she was at because she wasn’t in the yard with me,and then noticed she was eating something up on the deck.So I quickly went back up the stairs to see what was going on,and then noticed she was eating vomited,swollen nuggets of the dry dog food.I don’t know how much initially was vomited up because she was eating quickly when I got to her.After pulling her away from the vomited food,I counted 19 peices of food nuggets left over.The food nuggets are the small size ones,so there’s quite a few in each 3/4 cup/twice a day serving,so volume-wise dry it isn’t that much..but I don’t know how much she vomited initially before she ate some of it by the time I got to her..or if it makes any difference at all?

    What I’m not sure of here,is whether the dog food and Heartworm medication combination I gave her 10 hours earlier at 1:30pm was already far enough along in the digestive process,so the medication was fully absorbed by 11:30pm,and the food that she vomited was just from the later,second feeding at 8:00pm?…or if I’m going to need to re-dose her again?.


  9. Yes, we had some problems with our golden; vomiting after administering an oral heart worm preventative. We changed to different brands with no result… until finally it ended 🙂

  10. Thank you for sharing

  11. Hi, I had to go out of state for a family emergency for three months and I left my dog’s Sentinel flavor tabs back home. It has been three months since his last dose. Can I give him his next dose now or would that be harmful?


  12. I would proceed with giving the sentinel, and at your next yearly wellness exam at your vet, you can have your annual heartworm blood test

  13. Been sick and missed two doses of interceptor for my two dogs. Is it ok to go ahead and give it to them now? Please advise

  14. I dont have any problems simply restarting the medication interceptor. Use monthly and follow your local vet’s recommendation, in terms of the next annual heartworm test due, etc. But no problem in simply restarting the medication now

  15. We’ve been out of state since Christmas off and on, and I can’t remember when I last gave my cats their revolution. Is it OK to give it now? The vet said I need an appto. For it and we’re leaving again to visit a sick relative. My cats are indoors in Central Texas.

  16. HI Jen. I dont see a problem in reapplying the revolution now on your cats. Speak to your vet, however, as not sure why they dont want to ok that for you(it is a prescription item), but your cats are indoors, etc and there are minimal risks

  17. I have a question about storage of Heartgard medication. It says on the box to store at 68-77F with “excursions” between 59 and 86F permitted.
    My question is, how long can the meds be exposed to a higher temperature? Have you ever heard of them losing potency or going bad if overheated?


  18. I cant tell you definitively how long the higher temperature exposures are ok; it may be best to contact the drug manufacturer and ask this specific question to their customer support

  19. I was supposed to give my dog heartgard on the 2nd of November, but I forogot. It is now the 28th of November and I will not be able to get more heartgard until tomorrow. When I get the heartgard is it okay to give to my dog?

  20. HI Holly. It is fine to just go ahead and give the next dose of heartguard when you get it. No worries.

  21. do dogs need to chew the chewable in order for them to be effective? I have a gulper that doesn’t chew anything. we are on heartgard plus and I can’t get a straight answer from the manufacturer. they say it says encourage chewing on the package labeling but I get conflicting stories as whether it is for choking purposes or because it is not effective if not chewed.

  22. From my knowledge and understanding of it, it does not matter whether product is chewed or not. it just comes in that formulation to make it easier for the patient. As long as you administer the whole contents of the chewable in any way that you can, I dont think that will be a problem, however may be best for you to call manufacturer and ask for technical support and/or veterinarian on staff with that company, who can provide you with definitive and expert opinion on their product

  23. My 11 year old Maltese has Cushings disease and it is time for his heart worm vaccination. Does he still need this vaccination at his advanced age or should I skip it at this time.

  24. In my opinion, I am NOT a fan of the 6 months Proheart injection(if that is what you are referring to), in pet this age, and with this type of chronic disease. I would ask your vet about long term and very safe oral meds like heartguard. AS for other vaccinations, STAY away from non essential puppy parvo/distemper vaccinations as your pet is not at risk for these especially at this age, and if he was vaccinated as a youngster.

  25. My dog had her last heartworm test in September 2019. Negative. She received her dose on Oct 17 2019. I have not given it to her since then because she had a bad UTI and was having terrible diarrhea and upset stomach due to allergies. Is it ok to give her a dose now that she seems better without getting another heartworm test.?

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