First U/S all normal but no heartbeat

Hi ladies! I'm 6w4d and had my first U/S today. Everything looks great but she couldn't detect a heartbeat.  I have fibroids so my doc said they could be blocking some of her view (took a long time to find sac, yolk, and fetal pole).  She's not worried, but obviously I am!  I have another U/S scheduled in 9 days.  Anyone else not hear a heartbeat this early and hear it later??