The ♥ icon is used all over the world as a pictogram of the human heart, and as shorthand for affection: ♥ = heart = love. It is the most commonly recognized symbol on the planet after the cross and the crescent. But though we see it all the time, and teach its meaning to our children, its associations with the organ of circulation, and indeed love, are neither ancient nor instinctive. The ♥ shape has represented a variety of things across different cultures over time, ranging from genitalia to cosmic wisdom; the heart, meanwhile, was an enigmatic organ for most of history, whose biological function was not understood until 1628; and the emotion of love, if associated with flesh instead of mind or spirit, was equally likely to be linked to the eyes, the head, or the liver as to the heart. The story of how the ♥, the heart, and love came together is a romantic tale. Progress towards union was tortuous and was influenced by, amongst other matters, herbalism, heraldry, phallus, breast, and buttock worship, the philosophers of antiquity, the devotions of the Roman Catholic church, the introduction of the penny post, and fashions in playing cards and confectionary.

The ♥, in geometric terms a cardioid, is common in nature. It appears in the leaves and flowers of various plants, it is formed by swans when they touch beaks, by doves as they unfold their wings, by strawberries, cherries and beetroots in cross section, and is suggested by various portions of the human anatomy. Our most distant ancestors painted it on the walls of caves, but what it meant to them is unknown. As for the heart, the ancient Egyptians were the first civilisation to leave us a theory of its purpose: it was the part of the body where the soul and intellect of its owner resided, and, unlike the other internal organs which were extracted during the process of mummification, was left inside the corpse after death, so that the Goddess Ma’at might weigh it against the feather of truth in the afterlife and punish the heavy-hearted. The organ itself was portrayed in Egyptian visual art as a scarab, or dung beetle.

The ♥ entered Western iconography via the Greeks, who used it depict ivy or vine-leaves, respectively the symbols of constancy and regeneration. Carnal love, in contrast, was represented by the figure of the god Eros, who was usually portrayed as a naked boy armed with a bow and arrows. When Eros wished to curse or bless people with the emotion that he ruled, he aimed his darts at their eyes rather than their breasts, and they felt its effects throughout their entire bodies. The physical heart, meanwhile, was reckoned by Aristotle to be the seat of reason, and this view prevailed until the days of the Roman physician Galen, who decided rather that it was responsible for the emotions, with the exception of love, which resided in the liver.

Such confusion over the meaning of ♥, the purpose of love, and the function of the heart was compounded by the arrival of Christianity. Whilst Christians followed Judaic lore vis a vis the heart, which held that it was home to all our feelings, and which littered its sacred texts with references to the glad-, the kind-, the heavy-, and the hard-hearted, they decided that love was a metaphysical concept which had nothing to do with the world of the flesh or any part thereof. They did, however, adopt the ♥ as an icon of the vine, the Classical symbol of rebirth, and used it on their tombs to symbolise the hope of resurrection in the days when they were persecuted and their worship was clandestine.

However, the pagan tribes of Europe who converted to Christianity in the dark ages had different thoughts about the purpose of the heart, which they generally associated with courage, and alternative meanings for the cardioid shape. In the eastern parts of the continent, the latter was used on horse amulets, and depicted the path of the sun through the heavens over the seasons. The triquerta carvings of the Celts, meanwhile, which also resemble the ♥, are thought to represent eternity, and the similar Viking valknut design symbolized the power of the god Odin to induce battle-madness in warriors. However, as these disparate cultures became united under the cross, they also developed a common secular iconography, and the first link between affection and the cardiod shape was established in the medieval era, with the arrival of the concept of Courtly, or Romantic, love.

Courtly love, which put women on pedestals and men on their knees, is thought to have been picked up by Crusaders from the Islamic world, which had similar conventions in its poetry. The ♥, indicating steadfast love for a damsel, and derived from the ivy leaf of Classical Greece, was chosen to be its device and appeared in various colours—green, blue, red, and black—on the shields and banners of knights. The prim adoration the device represented was defined by the poet Andreas Capallenus in 1184 as “the pure love which binds together the hearts of two lovers with every feeling of delight.” Capallenus’s notion that the heart was the seat of affection was accepted by the gentry, and led to the practise amongst various royal families in Europe of commanding that their hearts buried in different places to the rest of their remains. Whereas their bodies were entombed in family crypts, their hearts were interred in a spot which had personal associations of happiness. King Richard the Lionheart of England, for instance, had his leonine organ buried in Rouen and the rest of his body laid to rest at the feet of his father in Anjou. However, this fashion provoked the ire of the Church, which issued a decree in 1311 stating that the soul did not reside in the heart alone, but was evenly distributed throughout the body.

Indeed, the Church fought the world of the flesh for possession of the cardioid symbol, the definition of love, and the purpose of the heart for much of the middle ages. Its attempts at dominance were spearheaded by a doctrinal innovation—devotion to the Sacred Heart, which manifested the love and suffering of Jesus Christ. Female devotees were especially prone to visions of the divine organ. They were led by Saint Gertrude who had a hallucination in the late thirteenth century during which she rested her head on the chest of Jesus and heard his heart beat. She asked St John, also present in her vision, if he too had enjoyed those “delightful pulsations” when he embraced Christ at the Last Supper, and the apostle confirmed he had, but had kept quiet about the sensation, because its revelation had been saved for a time when the world had grown weary and cold and needed such surprises to rekindle its love. Saints Mechtilde & Marguerite continued Gertrude’s good work, and established the beating heart of Jesus as symbolic of the love He had for mankind .

The visual iconography of the Sacred Heart was developed during the Counter-Reformation, which emphasised those parts of Christianity that required faith to imagine. Paintings appeared showing Christ opening his robe to reveal a ♥ shaped heart, or the same, solo, encircled with a crown of thorns, and topped with a halo and another crown of gold. The church also developed a reciprocal doctrine: the Immaculate Heart of Mary, which symbolised the love of mankind for their Saviour, and encouraged the production of images in which Mary too displayed a radiant organ.

However, the Church did not achieve its desired monopoly over the cardioid. It was thwarted by the appearance of a new use for the symbol, which put it in front of more people’s eyes than ever before. In 1480, shortly after the appearance of the printing press, the commercial manufacture of playing-cards commenced in France. Printed cards used hearts as their second suite instead of the cups, representing the Holy Grail, which hitherto had appeared on hand-painted decks. Whilst the hearts on cards maintained a sacred connection—the four suites were analogous to the Medieval feudal estates: spades, which had been swords, symbolised the gentry; hearts, which once were grails, the clergy; diamonds spoke for the merchants; and clubs were linked with agriculture and hence the peasantry—they were employed in a profoundly secular context. People associated the symbol with gambling instead of love, whether for God or vice versa.

Indeed, beyond Courtly Love and Sacred Hearts, the palaces of princes and the cells of nuns, pagan notions persisted in folk culture of what love was, and of what the ♥ meant. The common people were altogether more erotic, especially in their iconography. Their cardioid was a symbol of fertility and coition. It evoked breasts, buttocks and genitalia, and when they came across its likeness their minds turned to sex. In Shakespearean England, for instance, the plackett—a heart shaped apron for women with a pocket for the hands below the waist was also the slang name for a vagina. Such primal views bubbled up into the higher strata of society during the Renaissance. Eros (or Cupid, his Roman equivalent) who had been resurrected by artists as a model for the Cherubic order of angels, re-acquired pagan traits, as is evident in the Uffizi palace in Florence where a ceiling decorated for Piero the Unfortunate with new-school cherubs, shows neotenic cupids shooting arrows tipped with phallic ♥s at the bottoms of young men.

Although the church fought to reclaim both its cherubim and sacred hearts via the publication of the visions of St. Theresa, who confessed to have been pierced repeatedly in the heart by a divine arrow held by a winged angel until she moaned in ecstasy, it lost control of the cardioid. Its influence was further diminished by advances in anatomy, which had been stuck in a rut since the days of Galen. In 1498, Leonardo da Vinci produced the first accurate drawing of a human heart, instead of following prior convention and depicting it as a pine cone. Leonardo also made a glass model of the organ. Its biological purpose was explained in detail just over a century by William Harvey in An Anatomical Study of the Motion of the Heart and of the Blood in Animals, which described how the heart functions as a pump and circulates blood out through the arteries and back through the veins. This insight transformed the way the west thought about the human body.

Although people now knew that their hearts didn’t look like cardioids, and that the organ itself was little more than a pump, they still preferred to associate the pounding muscle beneath their ribs with the emotion that made it sprint, or stagger, and the ♥ acquired sentimental overtones, which were exploited by confectioners. As sugar became increasingly common in Europe during the eighteenth century, so the creation of sweets, pastries and cakes with this hitherto costly substance became widespread. In cultural centres such as Vienna and Paris the Rococo style, which emphasised the flamboyant and whimsical, was applied to sweetmeats for sweet-hearts. Cherries, whose paired fruits had long been a symbol for lovers, and whose cross-section is cardioid, were a popular ingredient and decoration of both bonbons and tarts, as too were strawberries.

Whilst the strawberry had been used as a food and medicine in Europe since the days of the Romans, it was expensive and temperamental plant, which might produce lush and glorious fruit one year, then small, green, and bitter berries for the next ten. However, as the English colonies in Virginia began to flourish, and Europe learned of the perfection and constancy of the new world strawberry, samples were imported. One had arrived in Paris by 1636 when a botanist described it as Fragaria americana magno fructo—the American Strawberry with the big fruit. The import was cross-bred with a female plant from Chile, resulting in the modern commercial strain. This was widely cultivated and strawberry slices on tarts, and heart-shaped strawberry cakes placed the ♥ symbol, with fresh associations, in front of an ever larger audience.

In consequence, a saccharine vision of the cardioid prevailed which was reinforced in the nineteenth century by the appearance of mass produced Valentine’s Day cards. Although handmade valentines had been in use for several hundred years, they were rare, and did not have a common iconography. The first printed example, manufactured in England in 1840, shows a pair of seated lovers, and features a Romanesque cupid with a sacred heart impaled on his arrow hovering in the background. The habit of exchanging Valentine’s Day cards was boosted by the introduction of the penny post, and by the turn of the twentieth century, millions were being sent each year, most of which featured a ♥ somewhere in their designs.

Similar developments occurred in America, where greeting card manufacturers were sufficiently numerous to constitute a distinct industrial sector. There, too, the cardioid, meaning heart-felt love, was the most popular emblem on valentines. Such popularity continued into the roaring twenties, when American cards became a little less sentimental, and very much more prurient in their designs than their Victorian archetypes. Risqué versions pictured girls in one-piece bathing suits, with suggestive smiles on their faces, holding up heart-shaped pastries the size of frisbees. The concept of the love that the cardioid represented was also altered at about the same time by the appearance of psychoanalysis, which defined the emotion as a curious amalgam of the desire to commit incest and neurosis. This drift, however, was countered by the arrival of animated films. Cartoons found the cardioid shape to be a useful shorthand for affection, and indoctrinated successive generations of children with pulsing versions of the symbol, usually to signify an innocent mother love.

Whilst sentiment had enjoyed and won epic battles with the church and sex for possession of the heart, it had yet to confound medicine, which dealt it a potentially fatal blow in 1967 when the first heart-transplant was performed. Did you get someone else’s lovingness and lovability when you received their heart? Or was it really only a muscle, indifferent as to the identity of its owner? It seemed impossible to reconcile reality and romance in matters of the heart, so they separated. After the parting, the wounded sentimental version was debased by the commodification of its symbol.

In 1977 the New York State Department of Commerce commissioned Milton Glazer to create a marketing campaign for the city. The result was the pictogram I ♥ NY. At the time New York was a global capital of culture and Hollywood’s preferred location and very quickly people were wearing T-shirts saying I ♥ London or similar. The meaning of the symbol was diluted from love of another or of God or of a mother to enthusiasm for a place or an activity: the passionate commitment to a city, or a football team. The speed at which the symbol spread in its newest incarnation resulted in the creation of parodies, some of which, such as I ♣ my Wife, were antithetical to the spirit of romance.

Notwithstanding such abuse, and the increased, indeed relentless commercialisation of St. Valentine’s Day, the sentimental link between ♥ meaning heart and affection has triumphed in the contest with cynicism. Countless parodies have failed to discredit it, and the symbol has spread with ease around the world. In Japan, for instance, the Hello Kitty brand features a kitten-ness with a cardioid head, but without a mouth, for according to the brand’s owners “she speaks from the heart, having no need of any particular language.” Moreover, the American Greeting Card Association estimated that over a billion valentine cards were sent in 2009, implying that nearly one-sixth of the population of the planet choose to express their affection with reference to a particular iconography: &hearts equals heart equals love.

Interestingly, and to the disbelief of most medical professionals, evidence in support of the heart/love equation has surfaced recently amongst recipients of heart transplants, some of whom claim to have enjoyed post-operation changes in behaviour. Clarie Sylvia, for example, a tranquil health and fitness enthusiast, became “aggressive and impetuous” and developed cravings for beer and KFC, both of which she hated when possessed of her original heart, but which had been the favourites of her donor—an eighteen-year-old man who had died in a motorcycle accident—with beer in his blood and chicken wings in his pockets. Other recipients have demonstrated equally dramatic shifts in their affections. Perhaps the intuitive link between the organ and love, which we are reminded of each time we meet our lovers and our heartbeats speed, will one day be explained and saluted by science.