is it normal to not find a heart beat at 7weeks?

Steph

hi, I had a dating scan last Friday at 7 weeks and no heart beat was found. Dr told me I have had a missed miscarriage but wanted to scan me again in a week. I have my scan tomorrow and I'm so scared. I have already lost one baby, I dont want to loose this one either. Is it too early to find a heart beat at 7 weeks?