4 week old puppy panting a lot.?

I have a 4 week old mastiff pup that I had saved. He is 4 weeks today. He is playing , acting healthy etc. The only thing is, is that for the past couple days I catch him panting every now and then, and it's not really that warm in my home. It stays between 72-74 degrees. Is the breathing fast and sometimes panting normal? Also another question, What are signs and symptoms of heart worms? He has already been de-wormed by the vet but I doubt that gets rid of heart worms if its even possible for him to have at such a young age? Yes I know everyone is going to say take him to the vet, he is schedualed to be seen in 3 days I just wanted some imput from people with possible experience or thoughts. Thanks for all your help and thoughts!