Atria

Atria (atrium)

The atria (plural) are the two upper chambers of the heart. There is an atrium (singlular) on either side of the heart – one on the left, and one on the right.

• Right Atrium: This chamber collects oxygen-poor blood returning from the body.
• Left Atrium: This chamber receives oxygen-rich blood flowing back from the lungs.

The atria have thin walls and act like holding tanks for blood before it moves into the powerful lower chambers, called ventricles.

For more information about how the canine heart works, see our course on Mitral Valve Disease in Dogs.