Red heart balloon

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STANDARDS

NGSS: Core Idea: LS1.A

CCSS: Reading Informational Text: 2

TEKS: 6.3D, 7.12B, 8.3D, B.12A

The Symbol of Love

How the heart icon came to represent feelings of affection

AS YOU READ, THINK ABOUT the possible origins of common symbols you see around you.

Valentine’s Day is approaching, and love is in the air. Everywhere you look, there are heart-shaped cards, candies, and decorations. But February isn’t the only time you’ll see this famous shape. Heart icons appear year-round in advertisements, on clothing, and as emojis in texts. Pop stars even make the shape with their hands to express gratitude to fans at concerts. Across the globe, the heart is a universal symbol of love.

Valentine’s Day is near, and love is in the air. Heart-shaped cards, candies, and decorations are everywhere. But you won’t see this famous shape only in February. Heart icons appear all year in ads, on clothing, and as emojis in texts. Pop stars even make the shape with their hands to thank fans at concerts. Around the world, the heart is a common symbol of love.

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How did the heart come to represent love in the first place? Biologically speaking, your heart is a muscle. It’s responsible for pumping blood through your circulatory system, not for creating emotions—those come mainly from your brain. Also, you may have noticed that the cute heart emoji on your phone doesn’t look anything like the organ you’d see in a biology textbook. To discover the symbol’s origins, Science World delved into the history and science behind this beloved icon.

How did the heart come to picture love? In biology, your heart is a muscle. Its job is to pump blood through your circulatory system, not to create emotions. Those come mainly from your brain. Also, you may have noticed something about the cute heart emoji on your phone. It doesn’t look anything like the organ in a biology textbook. So, where did the symbol come from? To find out, Science World dug into the history and science behind this beloved icon.

BLOOD WAS ASSOCIATED WITH LOVE AND PASSION.

HUMOR ME

Some modern ideas about the heart stem from the beliefs of ancient Greek scientists, known as philosophers. They came up with theories about how the human body worked—many of which turned out to be incorrect. “Ancient Greek philosophers believed that the human body was controlled by four humors, or fluids: black bile, yellow bile, phlegm, and blood,” explains Brad Bouley. He’s a professor of scientific and religious history at the University of California, Santa Barbara.

To the ancient Greeks, a healthy person was someone who had all their humors in balance. They believed that too much or too little of any of these fluids caused physical, emotional, or psychological problems. Too much yellow bile was thought to make a person angry, while too much black bile made them depressed. Blood was the humor associated with love and passion. “The heart was seen as a motor that heated fresh blood and moved it through the body, so it was also viewed as the origin of passionate feelings,” Bouley explains.

Some modern ideas about the heart come from ancient Greek scientists, known as philosophers. They came up with theories about how the human body worked. Many of those theories turned out to be incorrect. “Ancient Greek philosophers believed that the human body was controlled by four humors, or fluids: black bile, yellow bile, phlegm, and blood,” explains Brad Bouley. He’s a professor of scientific and religious history at the University of California, Santa Barbara.

To the ancient Greeks, a healthy person had all their humors in balance. They believed that too much or too little of any of these fluids caused problems. These problems could be physical, emotional, or psychological. Too much yellow bile was thought to make a person angry. Too much black bile made them depressed. Blood was the humor linked to love and passion. “The heart was seen as a motor that heated fresh blood and moved it through the body, so it was also viewed as the origin of passionate feelings,” Bouley explains.

AN ENDURING SYMBOL

The scalloped shape of the modern heart icon may trace back to early scientific ideas about the body. “Ancient medical texts didn’t contain pictures, but Greek and Roman philosophers describe the heart as having two chambers [hollow spaces] and an indent in it,” says Bouley. “If you were to try to draw an organ based on that description, you can see how it might translate to the heart shape we see today.”

The modern heart icon has curves with an indent. This shape may go back to early scientific ideas about the body. “Ancient medical texts didn’t contain pictures, but Greek and Roman philosophers describe the heart as having two chambers [hollow spaces] and an indent in it,” says Bouley. “If you were to try to draw an organ based on that description, you can see how it might translate to the heart shape we see today.”

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It wasn’t until the 17th century that humoral theory was disproved. Scientists began to base their ideas about the human body on its anatomy, or structure. They discovered that the heart actually has four chambers that contract to pump blood through the body (see Heart Anatomy). “Scientific ideas about the body took hundreds of years to change,” says Bouley. But centuries of heart symbolism and imagery had already become part of our romantic traditions, appearing frequently in art, literature, and popular culture (see Key Moments: Heart Symbol Through the Ages).

Humoral theory wasn’t disproved until the 17th century. Scientists began to base their ideas about the human body on its anatomy, or structure. They found that the heart really has four chambers. These contract to pump blood through the body (see Heart Anatomy). “Scientific ideas about the body took hundreds of years to change,” says Bouley. But heart symbols and images had already become part of our romantic traditions. For centuries, they’d often appeared in art, literature, and popular culture (see Key Moments: Heart Symbol Through the Ages).

THE HEART SYMBOL FIRST APPEARED ABOUT 700 YEARS AGO.

THE HEART OF THE MATTER

Although the heart may not control our feelings, our feelings can have major effects on our heart. When you feel joy, like when you’re in love, your brain releases oxytocin and dopamine. These chemicals increase feelings of happiness and well-being. They also cause heart rate to increase and arteries to dilate, or enlarge. “This increases blood flow throughout the body, providing organs with more oxygen and improving their function,” says Dr. Ilan Wittstein. He’s a cardiologist, or heart doctor, at Johns Hopkins University in Maryland. “People who experience more positive emotions seem to have fewer heart problems in the long term,” he explains.

The heart may not control our feelings. But our feelings can have major effects on our heart. Take what happens when you feel joy, like when you’re in love. Your brain releases oxytocin and dopamine. These chemicals increase feelings of happiness and well-being. They also increase heart rate and cause arteries to dilate, or enlarge. “This increases blood flow throughout the body, providing organs with more oxygen and improving their function,” says Dr. Ilan Wittstein. He’s a cardiologist, or heart doctor, at Johns Hopkins University in Maryland. “People who experience more positive emotions seem to have fewer heart problems in the long term,” he explains.

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Negative experiences, like bad news or a heated argument, can affect the heart as well. “When a person is under stress, it activates the sympathetic nervous system,” says Wittstein. This system controls the body’s reaction to stress by releasing hormones, such as adrenaline. This chemical messenger provides a surge of energy, making you temporarily faster and stronger in case you need to fight or run from a dangerous situation. However, large amounts of these hormones can cause the tiny arteries in your chest to shrink, restricting blood flow to your heart. This can lead to chest pain and shortness of breath.

Negative experiences can also affect the heart. Some examples are bad news or a heated argument. “When a person is under stress, it activates the sympathetic nervous system,” says Wittstein. This system controls the body’s reaction to stress. It releases hormones, such as adrenaline. This chemical messenger provides a rush of energy. For a short time, it makes you faster and stronger. That helps if you need to fight or run from a dangerous situation. But large amounts of these hormones can shrink the tiny arteries in your chest. Then blood flow to your heart slows. This can lead to chest pain and shortness of breath.

WHAT IS THIS FEELING?

The connection between our brains and our hearts is complex, and scientists still aren’t sure exactly how the two interact. “Our scientific understanding of how our bodies and feelings are related is still quite basic,” says Wittstein. Everyone experiences emotions differently, making them difficult to measure. After all, how can anyone scientifically define a feeling as mysterious and complicated as love?

The connection between our brains and our hearts is difficult to explain. Scientists still aren’t sure exactly how the two affect one another. “Our scientific understanding of how our bodies and feelings are related is still quite basic,” says Wittstein. Everyone experiences emotions differently. That makes emotions hard to measure. After all, a feeling like love is mysterious and complicated. How can anyone define it scientifically?

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Although many romantic notions about the heart may be rooted in outdated science, the ancient Greeks’ theory that our feelings are connected to our physical well-being might not be that far-fetched. “People have always had an intuition that there’s a connection between their emotions and their hearts,” says Wittstein. “We’ve only recently started studying how our brains and our feelings can affect how our body functions,” he says. “This is really just the tip of the iceberg.”

Many romantic ideas about the heart may come from outdated science. But the ancient Greeks believed that our feelings are connected to our physical well-being. That theory might not be so far-fetched. “People have always had an intuition that there’s a connection between their emotions and their hearts,” says Wittstein. “We’ve only recently started studying how our brains and our feelings can affect how our body functions,” he says. “This is really just the tip of the iceberg.” 

COMMUNICATING INFORMATION: How has the scientific understanding of human emotions changed over time?

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