Rebecca Ann Ritter, Age 10, Of Allentown., Pa., for her question:
How often does the human heart beat?
Your little heart began to beat when you were an unborn baby, and it will. Beat, beat through every hour of your life, day and night. Its rhythm is sometimes faster and sometimes slower, depending upon the work it has to do. In an average year it beats over 37 million times.
The doctor clocks the rate of your heartbeat when he takes your pulse. He feels the throbbing beat of the blood pulsing through a large artery in your wrist and times the pulse on his watch, second by second. He figures haw many times your busy heart is beating in a minute, and if the pulse is faster than normal you mar have a fever.
A healthy heart whispers lub dub rest, lub dub rest with a steady rhythm. Each minute its pumping pulse pushes five quarts of blood on its way through the body. The never ending stream flows through a network of veins and arteries. If all these blood vessels were in a straight line, they would reach almost three times around the wide waist of the world. The pulsing heart must keep the circulation of blood going or the living tissues of the body soon perish from lack of oxygen.
The heart itself is a strong muscle. Its thudding beat is triggered by a built in wad of tissue ca11ed the pacemaker. This little timer starts each lub dub rest with ri0"orderb from the rest of the body. However, the rate of the heartbeat can be speeded up or slowed down on orders from the nervous system. The body orders the heart to beat faster when it is sick, after hard exerc7.se or when the emotions feel excitment, such as fear or panic. The heart is ordered to slow down when the body rests or sleeps.
The pulse then varies, depending upon how much blood the heart must pump through the body. It also varies as you grow up and grow older. The heart of a baby may beat 120 to 140 times a minute. The average heartbeat of a seven year old person is 90 times a minute. At age 10, your normal pll1.se varies from perhaps 70 to 100. Mlen you become an adult, it may vary from 50 to 87, and when you become an old person, it may vary from 50 to 67. Your pu1se as a girl will be a bit faster than that of a boy or man of your awn age.
Throughout life, the human heart beats an average of 72 times a minute, which is about 4300 times an hour. In a year, the wonderful muscle is expected to beat some 37 million times. In a long and healthy lifetime the human heart may beat between two and three billion times.
Since the heart never stops its whispering lub dub rest, lub dub rest, you would expect it to tire. It does not become weary because of the short rest period built into each throbbing pluse. The mighty muscle lub dubs and relaxes on an average of 72 times each minute. If all these rest periods are added up, we find that'the heart rests 15 hours and works; lub dub, lub dub, only nine hours each day and night.