atrium

In architecture, an open inner courtyard. An atrium was originally the central court or main room of an ancient Roman house, open to the sky, often with a shallow pool to catch rainwater.

atrium

Either of the two upper chambers of the heart. The left atrium receives freshly oxygenated blood from the lungs via the pulmonary vein; the right atrium receives deoxygenated blood from the vena cava. Atrium walls are thin and stretch easily to allow blood into the heart. On contraction, the atria force blood into the thick-walled ventricles, which then give a second, more powerful beat.