The first organ to form inside a human fetus is the heart. And new research says that heart might start beating earlier than we previously thought it did.
A team of U.K. scientists just published a paper pinpointing at what stage of development a heartbeat begins.
The study examined embryos in lab mice, looking at the formation of the tube-like structure that eventually develops into the heart.
But the researchers recorded coordinated pulses of calcium during that structure's development — they say those pulses actually produce the first heartbeats.
The study records the first heartbeat at 7.5 days after conception for lab mice — the Daily Mail says that's about 16 days for humans. It was previously thought that the human heart started beating about three to four weeks after conception.
Understanding how the heart forms during pregnancy could give scientists a better understanding of how heart defects form. It could also lead to better methods of repairing cardiac damage.
Lead researcher Paul Riley told the Daily Mail, "We are one step closer to being able to prevent heart conditions from arising during pregnancy. We also hope that this new research will help us to learn how the beating of new heart muscle cells might be triggered in replaced muscle after a heart attack."
The research was published in the open source journal eLife, and it was funded in party by the British Heart Foundation.