By 8 weeks a fetal pole & heartbeat should be detected. I hope that maybe things were positioned wrong and that it was just not able to be seen. We saw the hb & fetal pole at 6 weeks. I wish you the best of luck..
Well, you haven't miscarried, yet, if you are at risk for it..So they guessed you were 8 weeks..? well, what are your cycle dates? it could probably help.. if you are about two weeks, maybe even a week and a half off on your dates, it could be too early.. it is often too early to hear a heartbeat at around 6 weeks, sometimes up until about 7. I wouldn't worry toooo much, until you are totally sure.