I didn't have the exact same problem, but during my first pregnancy - at about 6-7 wks, my baby's heart rate was around 113, the yolk sac was too big and a funny shape - not round. All signs pointed towards an impending m/c and I was terrified for a few days until my next US which showed a normal size/shaped yolk sac and FHR at 140s. My baby is now 2! Hope that gives you some hope. Keep us posted. Good luck to you - it's such an awful feeling.
Thank so much. It is nice to hear a story that does not end in doom and gloom. It is going to be a long week and a half until my next ultrasound.