Copy/pasting different sentences from different articles you find online is plagiarism. Don't be a thief.
It is a muscular organ about the size of a fist, located just behind and slightly left of the breastbone.
https://www.webmd.com/heart/picture-of-the-heart
Researchers from the University of Oxford in the UK have shown that the first contraction of the heart muscle occurs 7.5 days after conception in mice, which they extrapolated to be as early as day 16 in humans.
https://www.sciencealert.com/first-of-our-3-billion-heartbeats-happens-sooner-than-we-thought
In a heartbeat you got a !BEER