My doctor tried to hear the heartbeat on a doppler at 15 weeks & 5 days and couldn't find it, she said not to worry about it because sometimes they can't get it until 17 weeks. I called her a few days later and asked for a scan because I was worried she couldn't find a heartbeat. She sent me for one, there was my bouncing little bubba with a excellent heartbeat. The ultrasound woman said she probably can't find it because my bubba was very active and kept moving. So it can be a while before they find it, and sometimes the baby doesn't always want to be found .