The term 'cardiac chambers' refers to the four chambers of the heart, which are the two atria and the two ventricles. The atria, which are the two upper chambers of the heart, are often referred to as the left and right atrium, and they are abbreviated as ATRIA (5 letters). The atria are responsible for receiving oxygen-rich blood from the lungs and pumping it into the ventricles. The ventricles, which are the two lower chambers of the heart, are responsible for pumping oxygen-rich blood out of the heart and into the body. Together, the four chambers of the heart work together to ensure that oxygen-rich blood is circulated throughout the body.