Medical and reproductive health experts say the reference to a heartbeat is medically inaccurate as an embryo does not have a developed heart at six weeks’ gestation.
Flickering that we see on the ultrasound, that’s super early in the development of a pregnancy, is actually electric activity. And the sound that we hear at that point is actually manufactured by the ultrasound machine.
An embryo at six weeks’ gestation is only about four weeks old, because the pregnancy clock starts at the parent’s last menstrual period. Most people don’t realize they are pregnant until after they have missed a period, two weeks after conception.
https://www.texastribune.org/2021/09/02/texas-abortion-heartbeat-bill/