The organ that circulates our blood still retains rich emotional and cultural significance.

Five hundred years ago the Aztecs of Mexico 'fed' their gods with human hearts, which a priest cut, still beating, from the living chest of captives held down on a stone slab by other priests. Once the heart had been cut out, it was placed in a bowl held by a statue of the god who was to receive it, and the victim's body was thrown down the temple steps. Some estimates suggest around 20 000 humans - usually captives from surrounding states - were sacrificed in this way every year.

Contrast this to events in 2007, when over 200 visitors attended the very first interactive broadcasts of live open-heart surgery at Wellcome Collection. Television cameras and a two-way radio link meant the viewers in London could watch whilst a world-leading cardiologist mended a patient's mitral valve at Papworth Hospital in Cambridgeshire. They asked him questions about what he was doing, and he replied in real time, as if the viewers were actually there in the operating theatre with him. The popularity of the event reflects the important place that organ holds in both our bodies and culture.

Indeed, back in antiquity, philosophers had already identified the heart as not only critical to our physical survival, but also as having profound emotional significance. Aristotle noted that it was the first organ to form in chick embryos - and believed it was the centre of vitality and intelligence - while Galen stated that the brain, not the heart, was the centre of consciousness and reason. However, he agreed with the prevailing idea that the heart was the source of the body's heat.

Over a thousand years later, Leonardo da Vinci also believed that the heart generated heat. Like Galen he was prohibited by law from dissecting human cadavers, so he used oxen and other animals instead produced his anatomical drawings of animal organs in an attempt to determine the structure and function of human organs.

It was the English physician, William Harvey, personal physician to Charles I from 1618, who is credited with being the first to correctly describe the properties of blood being pumped around the body by the heart. In one of his experiments, he 'milked the vein downward' to demonstrate its one-way action.

Four hundred years on, and technology has advanced dramatically. Not only have we the ability to perform open-heart surgery and broadcast it to viewers in another town or country, but today - thanks to Wilson Greatback who invented the first implantable cardiac pacemaker - over 20 000 people receive artificial pacemakers to regulate their heartbeats each year in the UK.

Although we now know that the brain is the seat of our intelligence and emotions, the heart remains the compelling metaphor for feeling - especially for love, or the end of love. Words and phrases such as 'heartfelt', 'with all my heart' and 'broken hearted' are still prevalent in literature and popular culture, while a heart is still the predominant symbol on Valentine's cards. Poignantly, during the 19th century, mothers who had to give their children up to foundling hospitals, used to leave half a hearts playing card with their baby, keeping the other half themselves, so that they could, if possible, claim the child back in the future. The torn heart represented the heartbreak of having to abandon the child - as well as the lifelong love the mother would feel for that child.

The heart has a moral significance too. The ancient Egyptians believed that once they died their hearts would be weighed against 'the feather of truth' to determine whether the deceased had lived nobly and truthfully, and could therefore participate in the afterlife. A heavy heart indicated a heart weighed down by a badly lived life, and was passed to the 'devourer of souls'. A light heart indicated a good person, who was then led to enjoy eternity in the 'happy fields'.

It is in our chests and stomachs that we feel both emotional pain and the glow of happiness - although we know these feelings stem from chemical changes in the brain - which perhaps is why the heart remains such an important symbol to us, despite everything science has taught us.