You doctor should let you know if there is anything to be concerned about. Don't be afraid to ask questions. Your doctor may plan to do a follow up ultrasound to make sure the heart rate has gone up to the 100's. You should call your doctor today and ask your question. You'll feel better having the answer than waiting until your next appt.
Good Luck!
This is something that I would ask a doctor. I ask my doc a TON of questions. I cant say whether its normal or not. Get a notepad, and every time you have a question, write it down so when u see the doc again nothing slips your mind : )