Please give your puppy the heartworm pills each month start asap. Not only the treatment does not come cheap, and it is VERY PAINFUL for dogs and it could cost their lives. I cried so many times just watching Zack, he was in so much pain, he would not want to eat, to walk,and his whole body was trembling. And I could not help him at all, just watching. You have to keep them really quiet after the treatment for few months. My Zack will go to another treatment this Friday. If you please read heartworm treatment and the reaction to the treatment, believe me, you don't want your dear dog to go through this horrible procedure.
My previous dog (also a golden) had the pill every month all her life, she loved the pills.