The heart is a pump, and the blood goes round, and round, and round all the time. And why does it do that? Why can't it just have a rest? Well, the blood has to be kept moving around all the time ...

Narrator: Well here we are ladies and gentlemen, in the heart, the powerhouse of the circulatory system, the hardest working muscle in the entire human body! Your heart first pumps blood to your lungs ...

Until 1628 few Europeans disputed the teachings of Galen, an accomplished Greek physician and scholar. Galen lived in the second century A.D., and his teachings would come to dominate European ...