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it will take a babys heart 40 days or 6 weeks to develop it will go through a phase called looping. Then when the baby is born after its first breath the valves in vetro are closed and the ones used in life open. Since the baby is using its owns lungs now. The last valve should close about a week after birth, leaving the 4 other valves open.
Really early on one of the first things that is formed is the beginnings of its heart and circulatory system. Once it starts pumping the blood starts flowing.

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8y ago

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