What do the atria do in the human heart?

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Illustration of a human heart cross-section showing four chambers-left and right atria and ventricles-with labeled major blood vessels. An inset highlights cardiac muscle tissue, showing myocytes and intercalated disks. — human cardiovascular system The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.

In the human heart, the atria are the two upper chambers responsible for receiving blood and driving it into the lower chambers, known as ventricles, which then pump the blood away from the heart.1

The two atria function as follows:

Right Atrium: This chamber receives deoxygenated blood—which is low in oxygen and high in carbon dioxide—from the body via the superior and inferior venae cavae and the coronary sinus. It then transfers this blood into the right ventricle to be pumped to the lungs.1
Left Atrium: This chamber receives oxygenated blood from the lungs through the pulmonary veins. It then directs this blood into the left ventricle, which pumps it through the arteries to the rest of the body's tissues.1

Each atrium features an ear-shaped projection called an auricle, which should not be confused with the entire atrium itself.1