Heart
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The heart is a very importaint organ that is used to pump blood around the body. The heart is a ball of [(muscle)] about the size of your fist. It is a special type of muscle which never tires. Try clenching your fist once a second. you probably won't be able to do it for long. The heart sends the red [blood] cells that are empty to the [(lungs)] and when the blood comes back again, it pumps the blood back around the body.