The Heart

1. A system that sends electrical impulses to the heart in order to set the heart rhythm
4. Each of the two upper cavities of the heart from which blood is passed to the ventricles. The right atrium receives deoxygenated blood from the veins of the body; the left atrium receives oxygenated blood from the pulmonary vein
6. Any of the tubes forming part of the blood circulation system of the body, carrying in most cases oxygen-depleted blood toward the heart
8. A partition separating two chambers, such as that between the nostrils or the chambers of the heart
9. A large vein carrying deoxygenated blood into the heart. There are two in humans, the inferior vena cava (carrying blood from the lower body) and the superior vena cava (carrying blood from the head, arms, and upper body)
11. A hollow part or cavity in an organ

2. Any of the muscular-walled tubes forming part of the circulation system by which blood (mainly that which has been oxygenated) is conveyed from the heart to all parts of the body
3. The principal involuntary-muscle tissue of the vertebrate heart made up of striated fibers joined at usually branched ends and functioning in synchronized rhythmic contraction
5. Any of the fine branching blood vessels that form a network between the arterioles and venules
7. A device for controlling the passage of fluid or air through a pipe, duct, etc., especially an automatic device allowing movement in one direction only
10. The main artery of the body, supplying oxygenated blood to the circulatory system. In humans it passes over the heart from the left ventricle and runs down in front of the backbone