Heart:The organ responsible for circulating blood from the veins into the arteries throughout the body. Situated in the chest cavity, it rests behind the breastbone and is positioned in front of the spine and trachea, while above the diaphragm. Typically, the heart is the size of a clenched fist, weighing approximately 298 grams or 10.5 ounces. Shaped like a cone, its tip points downward and to the left. About two-thirds of the heart is located on the left side of the chest, with the remaining portion on the right. It is made up of specialized cardiac muscle and consists of four chambers: two atria and two ventricles, each anatomically distinct. Blood enters the heart from the systemic veins into the right atrium, moves to the right ventricle, and is then pumped to the lungs. It returns to the left atrium, moves into the left ventricle, and is then driven into the systemic arteries. Functionally, the heart can be considered in two parts: the right heart and the left heart. The right heart includes the right atrium, which takes in deoxygenated blood from the body, and the right ventricle, which sends this blood to the lungs at low pressure. The left heart comprises the left atrium, which receives oxygen-rich blood from the lungs, and the left ventricle, which pumps this oxygenated blood to the rest of the body at high pressure.

CPR Certification Labs provides hands-on, American Heart Association–aligned CPR, BLS, ACLS, and PALS certification training to help providers master these life-saving skills.