An atrium is a large open space inside a building, often with a high ceiling and lots of light; in biology, it is one of the upper chambers of the heart.
It comes from Latin *atrium*, meaning 'central room of a Roman house'. The heart chambers were named by analogy, as central spaces where blood enters.
Roman houses centered life around the atrium, and modern buildings copy that idea with big, bright indoor courts. Your heart’s atria are like tiny inner courtyards where blood first arrives before being sent onward.
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