Is there another type of Heartworm injection other than ProHeart 6? My vet has given us the option of a yearly injection or tablets, although still got to have Heartworm test first. I just noticed on one of the threads a warning not to use ProHeart 6 but looking it up on google it says that is used every 6 months not annually and has been withdrawn? Of course I'll check out the name of the drug she is offering when I go back to the vets but like to be armed with any knowledge I can get beforehand.