6 weeks two days pregnant with no heartbeat found?

I went to the doctor today and had a sonogram, which showed the sac. I didn't think to ask at the time if she saw the pole. Then I had the internal sonogram done to find a heartbeat. And no heart beat could be seen. I am going back in 6 days to find the heartbeat. I am currently 6 weeks and 2 days pregnant and am very nervous. Is this normal to not find a heartbeat yet?