The principles of modern cardiology started in 1628 when William Harvey postulated most of our modern beliefs about the heart as a pump, and that it pushes the blood throughout our bodies.  However, consider this:  The human body has enough blood vessels within it, to circle the earth approximately three times. 

How is a one-pound organ with thin walls, powerful enough to push the blood in our circulatory system throughout this network of blood vessels?  And what pushes the blood forward after the exchange of gases at the capillaries of the lungs when the blood virtually comes to a stop?  If a heart is just a simple pump, why have artificial hearts been so difficult to perfect and have been relegated to no more than a bridge until a human donation?