The heart is divided into four chambers. The two upper chambers are called the atria. The right atrium and left atrium are separated by a wall of tissue called the atrial septum. The two lower chambers are called the ventricles, and are separated into the right and left ventricle by the ventricular septum. The ventricles have thicker walls and pump blood to the lungs and body.
Visit Houston Cardiovascular Institute Website for more information.