my dog has heart worms and i’ve been feeding it this medicine called interceptor. does this mean the medicine is working or something else is wrong?

The worm looked like a thin maggot. Does anyone know what kind it is? And do I have to take my cat to the vet, or can I get an over the counter med. Can my dog catch it? If I give my dog medication for worms, but doesn’t have worms, will it harm her?
Any info is greatly appreciated.