atrium

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atrium (ay-tri-ŭm) n. (pl. atria)
1. either of the two upper chambers of the heart. The left atrium receives arterial blood from the lungs via the pulmonary artery; the right atrium receives venous blood from the venae cavae. See also auricle.

2. any of various anatomical chambers into which one or more cavities open.
—atrial adj.

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