They are plastered all over candy and billboards. They're everywhere on social media and throughout pop culture. From jewelry to emojis, the heart icon has symbolized love for centuries.
But why?
Historian and Oxford professor Martin Kemp says it dates back to ancient and medieval times.
"There's no nice linear progression," Kemp said. "You can't say there's a big bang. It comes in erratically, in different times, in different ways, in different areas."
The first illustrations of a human heart go all the way back to ancient Egypt in 2500 BC.
In ancient Greece, philosopher Aristotle and physician Galen described the human heart as having three chambers with a dent, based on what they knew about animal hearts.
"They didn't see human hearts, but they knew about ox hearts, they knew about pigs' hearts, which they ate," Kemp said.
Kemp says these texts influenced future medieval artists in their drawings of the human heart.
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Other scholars argue the roots of the heart shape go back to the ancient Greek colony of Cyrene. They believe Cyrenians used the silphium plant as an early form of contraceptive, and the seeds look similar to the heart shape. Scholars believe the herb's association with love and sex might have given the heart its shape.
The Greeks weren't the only heart enthusiasts.
The Romans associated hearts with Venus, the goddess of love who — according to Roman mythology — set hearts on fire with her son Cupid.
Centuries later, the heart appears in biblical writings.
"The worship of the sacred heart of Jesus, which became very popular later with images of Jesus with the heart visible on his chest," Kemp said.
The Middle Ages saw a boom of heart illustrations inspired by ancient texts and the patron of love, Saint Valentine.
"In the 15th century, you begin to get to him, identified with love, with the life of a woman, for a man or man for a woman," Kemp said.
The first non-medical illustration accompanied the French poem "Le Roman de la Poire" circa 1255.
In centuries since, the heart icon has spread in art, playing cards and religious portrayals.
"But it really is 19th, 20th century, it becomes the standardized shape, and that is related particularly to Valentine cards," Kemp said.
To this day, the heart-shaped symbol hasn't skipped a beat.
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