My five-year-old dog has been on Heartgard for years. I missed a few months of treatment, and his vet said it’s too dangerous to refill without testing. That could make worms resistant, apparently. My last vet vehemently disagrees with this assertion. Is it dangerous?


Heartworms will not become resistant because you missed a few months. The dog may have become infected in that time, but it depends on how long the dog was off preventative and how long it has been since he stopped taking the meds. It takes about six months from the time is bitten by a positive mosquito until there are adult heartworms in the heart. The best thing to do would be to continue heartworm preventative and then test the dog later, at least six months after the time that he was off the preventative.

Updated on March 22, 2018

Original Article:

Why Your Dog Does Not Need a Heartworm Test Every Year
By Dr Mark