- Sep 23, 2010
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i think it is because if you give the the meds and the worms all die at the same time it will clog up the heart. but not 100% sureIf your dog has not been on heartworm meds already they will need to be tested first. I don't remember the particulars just that it is dangerous to give HW meds if they already have them. I never have problems w/ any of the
'vet" flea meds, but those you get from the store (not online vet meds) have never worked for me