Heart

The heart is a muscular pump. Oxygen-rich blood from the lungs enters the left side of the heart and is pumped to the organs. Veins carry the blood back to the right side of the heart. The blood is then pumped back to the lungs. A child’s heart is about the size of his fist. The heart has four chambers. The two upper chambers are the right atrium and the left atrium. The two lower chambers are the right ventricle and the left ventricle. The heart is separated lengthwise into the right and left sides by a wall called the septum. Four one-way valves control the flow of blood through the heart.
Oxygen is the energy used by the cells of the body. The right side of the heart receives blood that has been “used” by the body. This blood contains “waste” in the form of carbon dioxide and a low amount of oxygen. Blood comes to the right side of the heart through two large veins, the superior vena cava and inferior vena cava. The blood enters the right atrium, passes through the t...