People celebrate every St. Valentine’s Day using heart shapes. Greeting cards bear them, cakes and candies are made in this shape, and they’re used as decorations on anything connected with the holiday.
The shape—usually red, with two round lobes at the top and a point at the bottom—is idealized and only approximates what a human heart looks like. But how common it is raises a question for the modern mind: Why do we use it this way?
At least in the secular sphere, Valentine’s Day celebrates romantic love, but in modern medicine, the heart is just a set of muscles that rhythmically contract to push blood around inside our bodies. What’s the connection?
The answer, as you might expect, goes back quite a ways. People have always known the organs of the body. Between cutting up animals and cutting up other people, they were quite familiar with them. But they didn’t always understand their functions.
For example, today we associate thought with the brain. This is known as the cephalocentric (“head-centered”) hypothesis, but this view wasn’t dominant in history.
The Greek philosopher Aristotle (384-322 B.C.) was one of the best anatomists in the ancient world. He noted all the blood vessels around the brain and concluded that its function was to allow the blood from the heart to cool down (On the Parts of Animals 2:7). The brain was, in essence, a heat management organ.
On the other hand, there seemed to be a direct connection between the heart and mental phenomena. If you’re seized by a strong emotion—love, lust, fear, anxiety, excitement—your heart speeds up. In the absence of such emotion, it slows down.
Sometimes—particularly at moments of peak emotion—your heart may even “skip a beat.” (Technically, one chamber beats early, before it’s fully filled with blood, so you don’t feel the beat; then it over-fills as the normal cycle reasserts itself, and you feel a more pronounced thump.)
It thus became natural for people to associate the heart with mental functions like emotions and intellect. This is known as the cardiocentric (“heart-centered”) hypothesis.
Several other factors may have also contributed to this view, such as the fact the heart is hidden (like our mental functions), that it is at the center of our bodies’ extensions (suggesting it’s important), and that if it stops working, you die (associated with the spirit leaving).
Whatever the factors, the idea that the heart is the seat of the mind was common in ancient cultures. Thus, when the ancient Egyptians mummified you, they kept your heart inside your body, but they took out the brain so that its moisture wouldn’t cause the body to rot. This would have been done for the two ancient Israelites who we know were mummified, the patriarchs Jacob and Joseph (Gen. 50:2-3, 26).
The Israelites also accepted the cardiocentric model. Thus, a man is said to rejoice “in his heart” (Exod. 4:14) or to have his heart “broken” (Ps. 69:20)—an expression we still use today. Angry people have their hearts grow hot (Ps. 39:3), and hearts “melt” with fear (Deut. 20:8). The heart is the seat of courage (2 Chron. 17:6), and God may fulfill the “heart’s desire” (Ps. 21:2).
In addition to the heart being seen as the place of these emotions, it was also seen as the seat of the intellect. Thus, before the Flood, God saw “that every imagination of the thoughts of [man’s] heart was only evil continually” (Gen. 6:5), and when Abraham heard the prophecy of Isaac’s birth, he laughed to himself and “in his heart” said, “Shall a child be born to a man who is a hundred years old?” (17:17). This mode of language is even applied to God himself, for after the Flood, “the Lord said in his heart” that he would not curse the ground again because of man (8:21).
The cardiocentric model continued to be used in the New Testament. The heart is still spoken of as the seat of emotions. Thus, Paul tells the Colossians to sing “with thankfulness in your hearts to God” (Col. 3:16), and he tells the Thessalonians that he wishes God will “encourage your hearts” (2 Thess. 2:17).
The heart is similarly envisioned as the seat of the intellect. Thus, Simeon prophesies that through Jesus, the “thoughts from many hearts may be revealed” (Luke 2:35), and when the disciples argue about who is the greatest, Jesus knows “the thoughts of their hearts” (9:47).
The image of the heart continued to be prominent in the post-apostolic age. After the year 1000, devotion began to grow to the heart of Jesus. A prominent example is the Sacred Heart of Jesus devotion revealed to St. Margaret Mary Alacoque between 1673 and 1675. This devotion depicts Jesus’ heart surrounded by flames of love, with a crown of thorns and a cross above it, and a solemnity commemorating the Sacred Heart is celebrated on the third Friday after Pentecost.
Ordinary people continue to use language based on the cardiocentric model today, such as when we say that someone is “big-hearted,” “cold-hearted,” or “tender-hearted.” We may say that someone has a “heart of gold” or a “heart of stone,” or that he is a “bleeding heart.” People “learn things by heart.” And of course, the Grinch’s “heart was two sizes too small.”
We do this without even thinking about it, the same way we speak of the sun rising and setting despite what Copernicus and Galileo had to say. For us ordinary individuals, this doesn’t raise much of an issue. The presence of the cardiocentric model in folk expressions is no big deal.
But what about when it appears in Scripture or Church documents—like those approving the Sacred Heart devotion? Does it conflict with the cephalocentric model that regards the head rather than the heart as the seat of mental activity?
The cephalocentric model also has a long history. It actually pre-dates Aristotle, having been proposed by the Greek philosopher Pythagoras around 550 B.C. Fans of the theory included Aristotle’s teacher Plato and the Greek physicians Hippocrates and Galen, so it’s not as if the idea was absent from Western thought.
Following the Scientific Revolution, evidence mounted that the brain is more associated with thought than the heart, and by the early 1800s, neuroscience had developed to the point that cephalocentrism was firmly established.
The Church knew this, and so in 1899, Pope Leo XIII explained the Sacred Heart in symbolic terms, stating that “there is in the Sacred Heart a symbol and a sensible image of the infinite love of Jesus Christ which moves us to love one another” and that “whatever honor, veneration, and love is given to this divine heart is really and truly given to Christ himself” (Annum Sacrum 8).
Similarly, in 2024, Pope Francis stated that “devotion to the heart of Christ is not the veneration of a single organ apart from the Person of Jesus. What we contemplate and adore is the whole Jesus Christ, the Son of God made man, represented by an image that accentuates his heart. That heart of flesh is seen as the privileged sign of the inmost being of the incarnate Son and his love, both divine and human. More than any other part of his body, the heart of Jesus is the natural sign and symbol of his boundless love” (Dilexit Nos 48).
What about the Bible? Does the cardiocentric language it uses mean that the biblical authors didn’t understand the role of the brain and the heart? They lived before the Scientific Revolution, so they would not be expected to, and that’s not a problem from the perspective of biblical theology.
The Second Vatican Council taught, “Since everything asserted by the inspired authors or sacred writers must be held to be asserted by the Holy Spirit, it follows that the books of Scripture must be acknowledged as teaching solidly, faithfully, and without error that truth that God wanted put into sacred writings” (Dei Verbum 11).
It also taught, “For the correct understanding of what the sacred author wanted to assert, due attention must be paid to the customary and characteristic styles of feeling, speaking, and narrating that prevailed at the time of the sacred writer, and to the patterns men normally employed at that period in their everyday dealings with one another” (op. cit. 12).
We therefore must distinguish between what the biblical authors assumed to be the case and what they were asserting by the language they used. When Luke says that Jesus knew “the thought of [the disciples’] hearts” (Luke 9:47), he’s asserting that Jesus knew their thoughts, not that these thoughts were literally housed in their hearts.
We don’t know which school of thought Luke subscribed to. As an ancient physician, he may have been a cardiocentrist or a cephalocentrist, but either way, it was normal for people of his day to speak of thoughts as coming from the heart—as is often the case for us today. In any event, Luke is not trying to teach us a medical theory; he’s telling us that Jesus knew what the disciples thought, and this assertion—not any background assumptions in the way it is expressed—is what is guaranteed to be true.
On the other hand, we shouldn’t be too quick to assume a strict correlation between the brain and mental phenomena. In the first place, there’s what’s known as “the little brain in the heart,” or the intrinsic cardiac nervous system (ICNS). It’s about forty thousand neurons that help regulate the heart’s activity, and things like a racing heart can affect emotional states (e.g., by causing fear and panic).
Even more surprisingly, there is evidence from heart transplant surgeries that something more than the physical organ—at least information—is being passed between patients. In one example, neuropsychologist Paul Pearsall recounts the cases of men he refers to as Jim and Frank. Jim had bad lungs and received a heart-lung transplant. However, Jim’s own heart was still good and was given to Frank. After the transplant, Frank’s personality changed to be more like Jim’s, Frank began exhibiting Jim’s food preferences, and during intimate moments Frank began calling his wife by the name of Jim’s wife (123-124).
Ultimately, neither the heart nor the brain may be essential for mental activity. Consistent with Christian teaching on life after death, the evidence of near-death experiences reveals that people continue to have conscious experiences even during cardiac arrest, when the heart has ceased beating and brain activity goes offline within seconds. Yet people in this condition accurately report things happening around their physical bodies and even in other rooms of hospitals that they have no sensory access to.
All of this serves as a warning against reductionistic theories that would too closely tie the mind and emotions to physical organs like the heart and the brain. Given the complexity of what we observe, this whole area is—as it was in biblical days—a mystery.