Stevie Burton, age 12, of Elon College, North Carolina, for his question:

How many times a day does the heart beat?

The heart is a sturdy fist made of pliable muscle material. It is, without doubt, the body's most dependable worker, carrying on its duties day and night without orders or instruction. Its method of working is basically simple and the rhythm of its beating is a repetition of the same basic operation. The normal heart under normal conditions beats 70 to 80 times a minute. If you tested your pulse for an hour, you could count about 4,200 heart beats.

During an average day, the human heart beats about 100,800 times. In a year, it beats almost 37 million times. It has been estimated that the heart of a 50 year old man has completed about 1,839,600,000 pulsing beats. However, the heart rests a fraction of a second with each beat and these brief moments tot up to plenty of leisure time. During 24 hours of steady beating, the busy heart manages to snatch a total of about 15 hours