atrium

https://doi.org/10.1351/goldbook.10441
Each of the two upper chambers of the heart from which blood is passed to the ventricles.
Note: The right atrium receives deoxygenated blood from the veins of the body, the left atrium oxygenated blood from the pulmonary vein.
Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 728 [Terms] [Paper]