Well if you had a transvaginial ultrasound done then you should have probably seen and heard a heart beat by the 8th week. Most doctors don't use dopplers until the 10-12 week mark and most doctors won't use them before that point. Also, if you are measuring 8 weeks by ultrasound then it could be a problem but if you are going my your last menstrual period (LMP) then it is very possible that you ovulated late and therefore, are not as far along as you suspected. Definitely follow up with your doctor. Best of luck to you!
if you ovulated late you could be off on yor dates.
when i was 8 weeks from LMP (I was really about 6 weeks cause i ovulated late) i had a vaginal u/s, my gestational sac was measuring 6 weeks 5 days and there was no heartbeat detected, i went back 2 weeks later and saw and heard the heartbeat and she was moving!
did they measure the gestational sac, fetal pole, yolk sac etc????
Sometimes you dont normally get a heartbeat untill 8 weeks. And you probably wont hear it on a Doppler untill 10 - 12 weeks.
Having irregular periods doesnt effect the babie's heartbeat if thats what you mean.