The term 'heart chambers' refers to the two main chambers of the heart, the atria and the ventricles. The atria are the two upper chambers of the heart, while the ventricles are the two lower chambers. The atria receive blood from the body and the ventricles pump blood out of the heart to the rest of the body. Together, the atria and ventricles work together to ensure that the body receives the oxygenated blood it needs to function properly.