perhaps since my intellect is so low, maybe a picture of a beating heart at 6 weeks will help me understand.
semp
At this period, the developing circulatory system allows maternal- embryonic nutritive and gaseous changes at the chorionic villi.
It is well documented in the literature that, in healthy fetuses, the heart rate (HR) increases from 110 bpm at the 5th week of gestation to 170 bpm at the 9th week of gestation. From then on, there is a gradual reduction in the HR that reaches a mean value of 150 bpm at the 13th week of gestation. -
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3279166/The heart of an embryo starts to beat from around 5–6 weeks of pregnancy. Also, it may be possible to see the first visible sign of the embryo, known as the fetal pole, at this stage.
The heart of a fetus is fully developed by the 10th week. 5th week: The developing heart is made up of two tubes that have fused in the middle, creating a trunk with four tubes branching off. The heart begins to beat, and it may be possible to detect it using vaginal ultrasound. -
https://www.medicalnewstoday.com/articles/when-does-a-fetus-have-a-heartbeat.
Although the fetal heart begins beating as early as the 5th week after the LMP, your ability to detect it will be limited by your equipment.An ultrasound machine usually will enable you to
see a heartbeat by 5 to 6 weeks gestation if equipped with a vaginal probe. Abdominal ultrasound will usually see the heartbeat by the 7th-8th week of pregnancy. -
https://oacapps.med.jhmi.edu/OBGYN-101/Text/Pregnancy/fetal_heart_beat.htmFetal heart beat can be detected as early as 34 days (just under 6 weeks) gestation on good quality, high frequency transvaginal ultrasound, as a crown rump length (CRL) of as little as 1-2 mm.
If a fetal heartbeat cannot be identified with a CRL ≥7 mm using transvaginal scanning, then embryonal demise can be diagnosed 3,4. Demise can be confirmed with repeated scanning and serial quantitative beta-HCG. -
https://radiopaedia.org/articles/fetal-heart-beat?lang=us