You should definitely be right on target for a heartbeat! It usually shows up between 5 and 6 weeks - even if you turn out to be on the early side for the heartbeat, they'll be able to see how many sacs there are still. The heartbeat(s) will be a teeny tiny little flutter -- it's pretty amazing! We did something similar, so I know how exciting it is when you finally reach that result you've been praying for! The biggest congrats to you!!