Ivomec 1% old dog

I have an old heeler dog, I took her to the vet when she was about 6 years old to have her fixed. Vet told me she had heart worms real bad. I started her on ivomec for the "treatment" the first dose she got kinda sick acting. But after that it didn't bother her. Before the ivomec she was always coughing and not real active. I haven't really heard her cough and she is pretty active after I started giving her ivomec every month. She is about 9 years old now. I'm not a vet, and am not saying it's ok to give your dog ivomec, just my experience.