Your heart pumps enough blood through your body every day to fill a railway tank car. It exerts enough energy every twenty-four hours to shovel twenty tons of coal onto a platform three feet high. It does this incredible amount of work for fifty, seventy, or maybe ninety years. How can it stand it? Dr. Walter B. Cannon, of the Harvard Medical School, explained it. He said “Most people have the idea that the heart is working all the time. As a matter of fact, there is a definite rest period after each contraction. When beating at a moderate rate of seventy pulses per minute, the heart is actually working only nine hours out of the twenty-four. In the aggregate its rest periods total a full fifteen hours per day.