The heart is a muscular organ that pumps blood throughout the body. It is divided into four chambers: the right and left atria and the right and left ventricles.
The right side of the heart is responsible for pumping oxygen-poor blood from the body into the lungs, where it receives oxygen and gets rid of carbon dioxide. The right atrium is the upper chamber of the right side of the heart, which receives deoxygenated blood from the body through the superior and inferior vena cava veins. The right ventricle is the lower chamber of the right side of the heart, which receives the deoxygenated blood from the right atrium and pumps it into the pulmonary artery, which carries the blood to the lungs.
The left side of the heart is responsible for pumping oxygen-rich blood from the lungs to the rest of the body. The left atrium is the upper chamber of the left side of the heart, which receives oxygenated blood from the lungs through the pulmonary veins. The left ventricle is the lower chamber of the left side of the heart, which receives the oxygenated blood from the left atrium and pumps it into the aorta, which carries the blood to the rest of the body.
Overall, the atria of the heart are the upper chambers that receive blood, while the ventricles are the lower chambers that pump blood out of the heart. The right side of the heart is responsible for pumping blood to the lungs, while the left side pumps blood to the rest of the body.