The ________(1) is the organ in the human body that pumps blood to all the other organs, tissues, and cells. The heart is made up of four _______(2) chambers and valves. The right _______(3) receives deoxygenated blood from the body and pumps it to the lungs. The lungs add _______(4) to the blood and send it back to the heart. From there, the left _______(5) pumps the oxygen-rich blood out to the rest of the body. Within the heart are four valves _______(6) open and close to regulate the flow of blood. They are the mitral, tricuspid, pulmonary, and _______(7). The heart is controlled by an internal _______(8) system.

        1. Heart 
        2. Separate 
        3. Atrium 
        4. Oxygen 
        5. Ventricle 
        6. that 
        7. Aortic 
        8. electrical