Chambers

Blood returning from the rest of the body enters the heart through the right atrium, which acts as something of a storage bin. After collecting in the right atrium, blood enters the right ventricle. As the right ventricle contracts, it pumps the blood into the lungs, where it is enriched with oxygen. Pulmonary veins in the lungs then bring the oxygen-enriched blood to the left atrium, where it collects until it is pushed into the left ventricle, the main pumping chamber of the heart. The left ventricle pumps the blood through the aorta and into the circulatory system, where it is distributed to the entire body.

In a healthy heart, blood cannot flow between the right and left sides. The atria are separated by a wall called the atrial septum and the ventricles by the ventricular septum.