What Does a White Shadow on the Baby’s Heart and to Much Fetal Movement Mean?

They probably meant that the baby was moving too much to get an accurate heart measurement. When I had an ultrasound to check for heart defects, my baby was moving too much and they couldn't get an accurate reading. They sent me to a specialist, who had a better ultrasound.
They were getting a shadow because of the fetal movement. When the baby moves too much during the ultrasound, they get shadows, because the ultrasound is sound waves bouncing off the baby. When the baby is moving the waves get disrupted and cause a shadow. They were probably trying to be safe by sending her to a specialist, just to rule out a hole in the septum. That is what they did for me.