Unfortunately when this happened to me I also miscarried. In my case I never had a heartbeat at all, the baby had stopped growing around the 5-6 week mark. This certainly does not mean it will be the case with you, and I hope you have a better outcome then I. I would however be prepared just in case as Eirlis said. I wish you luck.
Unfortunately I have had this same thing happen twice in a row now. Both times there was a heartbeat at 7 weeks but the sac was still very small. I miscarried a few weeks later.
I'm so sorry you are going through this too. Hopefully you will be in the 10% that go on to have a normal pregnancy. However you should also start preparing yourself for the strong possibility that you will lose this pregnancy. Best of luck.