The heartThe heart is one of the most important organs in the entire human body. It's actually nothing more than a pump, a set of muscles that pushes blood throughout the body, beating about 72 times per minute of our lives. The heart pumps blood, which carries all the vital materials that help our body function and eliminates unwanted products that we don't need. The brain, for example, needs oxygen and glucose which, if not continuously received, will cause it to lose consciousness. Muscles need oxygen, glucose and amino acids, as well as the precise percentage of sodium, calcium and potassium salts to contract. regularly. The glands require adequate supplies of raw materials from which to produce specific secretions. If the heart stops pumping blood, the body begins to shut down and after a very short period of time expires. The heart is basically a muscle (a little bigger than a fist). Like any other muscle in the human body, it contracts and expands. Unlike skeletal muscles, however, the heart functions according to the "Law of all or nothing". That is, every time the heart contracts, it does so with all its power. In skeletal muscles the characteristic of "gradation" is present. The pumping of the heart is called the cardiac cycle and occurs about 72 times per minute. This means that each cycle lasts about eight-tenths of a second. During this cycle the entire heart essentially rests for about four-tenths of a second. Composition of the heartThe walls of the heart are made up of three layers, while the cavity is divided into four parts. There are two upper chambers, called the right and left atria, and two lower chambers, called the right and left ventricles. To the right... center of the paper... at the normal age of 70, we see that the cardiac output of a normal human heart over its lifetime would be approximately 1 million liters, or approximately 250,000 gallons (US) !It works Quotedhttp://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CCkQFjAA&url=http%3A%2F%2Fwww .webmd.com%2Fheart-disease% 2Fguide%2Fhow-the-heart-works&ei=34KBUpC5B-mKiAL9i4CQAQ&usg=AFQjCNH0xTJSyAkZk7vbV5cwezEx1hLzIw http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=6&cad=rja&ved=0CFE QFjAF&url=http%3A %2F% 2Fkidshealth.org%2Fkid%2Fhtbw%2Fheart.html&ei=34KBUpC5B-mKiAL9i4CQAQ&usg=AFQjCNFMzFAlWpk6TLHyYak4Y_VHOK2XnA http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd= 2&cad=rja&sqi= 2&ved=0CC0QFjAB&url=http%3A%2F%2Fscie nce.howstuffworks.com%2Flife%2Fhuman-biology%2Fheart.htm&ei=fIeBUqeWHMqliQK1xIFI&usg=AFQjCNGE3AHhdztxr-pLjajd_Fw4hoF8jQ