The four valves of the heart prevent blood from flowing in the wrong direction, and open or close each time the heart beats. Learn more about them, here.

The chambers of the heart operate as a ‘double-pump’ system for the body’s circulation. In coordination with valves, the chambers work to keep blood flowing in the proper sequence.

Leonardo da Vinci's studies of human anatomy were hundreds of years ahead of their time - and his detailed drawings of the heart still resonate today, says a book by a cardiac surgeon.