Heart

Image result for heartThe heart is the , or body part, that pumps blood                       through the body. It is the main of the                                           cardiovascular system. The cardiovascular system                               carries substances to and from all parts of the                                          body in the blood.

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The human heart is pear-shaped and slightly larger than a fist. It is located high in the chest, slightly to the left. The heart of a grown-up person weighs about 8 to 12 ounces (230 to 340 grams).

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The heart is made of very strong muscle. This muscle pumps blood by squeezing and relaxing in a regular rhythm. This rhythm is called the heartbeat. The heart muscle beats an average of 70 times per minute.

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Like the human heart, the hearts of mammals and birds have four chambers. The hearts of other animals are different. Amphibians and lizards have hearts with three chambers. Fishes’ hearts are folded tubes, with three or four sections that are like chambers. Spiders and some worms have hearts that are straight tubes.

Hearts can vary greatly among different types of animals. The hearts of mammals and birds have four…

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