t on a constant supply of oxygen. If the circulation to the brain is stopped, death ensues shortly. Since heart attacks are the number-one cause of death in the United States, the heart gets a great deal of attention. The role of the heart was long considered a mystery and often given elevated importance. Some thought it was the seat of the soul. Others thought it was the center of love, courage, joy, and sadness. Primitive man must have been aware of the heartbeat and probably recognized the heart as an organ whose malfunction could cause sudden death.

The hearts of primitive people apparently had only one atrium and one ventricle. Since their body temperature and metabolic rate fluctuated with the environmental temperature, they did not need as efficient a circulatory system as mammals and birds. The two-chamber heart is retained by modern fish, but oxygen-rich blood does not mix with oxygen-poo

Some common words found in the essay are:
SYSTEM Located, HUMAN HEART, EVOLUTION HEART, , heart muscle, body temperature, human heart, circulatory system, connective tissue, left half, birds mammals, thin layer, oz blood, qt minute,
Approximate Word count = 609
Approximate Pages = 2 (250 words per page double spaced)