Your heart is a muscle that sits in your ribcage between your lungs. It acts as a pump, keeping you alive. It does this by continually pushing blood, carrying oxygen, to all the cells of your body through blood vessels. Your body tells your heart how much blood to pump, depending on how much oxygen it needs at any particular time. For example, when you are asleep you don't need as much oxygen as when you are playing sport, so your heart doesn't need to pump as much blood .

Sumerians (from 5000 BC) thought that the heart was the centre of thought.

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