CHAPTER 11 - Heart science

The human heart: the metaphorical source of our feelings and expressions, an emotional enigma that is both a generator of love and its barometer.

It’s said that you can have a heart of gold, a heart of stone, a heart of devotion or a heart of compassion.  You can be kind hearted, broken hearted, or heartless.  Your heartstrings can be tugged, and you can wear your heart on your sleeve.  Your heart can be in the right place, or you can be young at heart.  You can win someones heart, lose heart, or set your heart on something or someone.  Your heart can skip a beat or it can figuratively stop beating. 

The heart is so revered by humanity that references to it pepper all aspects of our culture, from historical literature to popular music and everyday conversation.  Such cultural reverence isn’t given to other important parts of the body such as lungs or kidneys.  When was the last time someone said, “I love you with all my spleen.”  Or, “That guy has a pancreas of gold!”

The history of medicine explains some of the reasons why the heart has become synonymous with love and emotion.  Ancient Babylonians thought that the liver was the center of feelings and emotions; the heart was the center of the mind; the stomach was the center of strength and courage.  The ancient Egyptians, on the other hand, thought that the heart was the center of feelings and emotions, a position that Greek and Arab physicians then adapted, and Roman physicians like Aristotle and Galen took as fact [252].  But it was a man named Herophilus, a Greek physician working in Alexandria, Egypt, around 300BC, who set things straight.  With rigorous anatomical studies on the nervous system, he proved that the brain and not the heart was the seat of intelligence.  But the idea of the heart as our emotional centre never left the philosophical and literary worlds, and thus, the concept still lives on today.

The Egyptian belief that individual organs were responsible for emotions and diseases also lead to other theories, the echoes of which still linger in our modern medical and literary works: “The first mental disorder attributable to women, and for which we find an accurate description since the second millennium BC, is undoubtedly hysteria. The first description referring to the ancient Egyptians dates to 1900 BC (Kahun Papyrus) and identifies the cause of hysterical disorders in spontaneous uterus movement within the female body.” [253]

In other words, the ancient Egyptians believed that only women suffered hysteria, because they thought the uterus would move around the woman’s body, disrupting the action of other organs and causing symptoms.

As noted by Tasca et al, “We also find indications of the therapeutic measures to be taken depending on the position of the uterus, which must be forced to return to its natural position. If the uterus had moved upwards, this could be done by placing malodorous and acrid substances near the woman’s mouth and nostrils, while scented ones were placed near her vagina; on the contrary, if the uterus had lowered, the document recommends placing the acrid substances near her vagina and the perfumed ones near her mouth and nostrils.” [253]

Somehow I can’t imagine a woman already stricken by panic would be helped, in any way, by a bunch of men pushing rotten meat under her nose and flowers at her genitals.

Thankfully, medicine has progressed since then, and the idea that Herophilus proposed three hundred years before the birth of Jesus - that the brain is the centre of all thought and emotion - has become the mainstay of medical thinking.

However, Dr Leaf would have us believe that there is still some truth in an ancient notion more than two thousand years old.  She writes that, “Toxic stress is particularly powerful because your heart is not just a pump.  It is actually like another brain.” [1: p40]

She continues: “It is proving to be a real intelligent force behind the intuitive thoughts and feelings you experience.” [1: p40]

And: “The signals your heart sends to your brain influence not just perception and emotional processing, but higher cognitive functions as well.” [1: p41]

So how does the “mini-brain” function?  She explains in chapter 6, “Your heart is in constant communication with your brain and the rest of your body, checking the accuracy and integrity of your thought life.   As you are about to make a decision, your heart pops in a quiet word of advice, well worth listening to, because when you listen to your heart, it secretes the ANF hormone that gives you a feeling of peace.” [1: p62]

She repeats the same information nearly word-for-word in her new book [2: p177].  So these ideas are something that she still believes in.

To summarise, Dr Leaf believes that the heart provides inner peace and influences higher cognitive functions through the nerves between the brain and the heart, and the chemical called ANF.  Despite Dr Leaf’s claims that this concept is a scientific breakthrough, mainstream science does not agree with her.

First, lets look at the arguments that Dr Leaf proposes to support her position, and then I’ll outline the evidence from modern clinical science that both contradicts Dr Leaf’s theory, and demonstrates the real physiology of the heart and the brain together.

“Evidence” for the heart as a mini-brain

In her 2009 work, Dr Leaf bases her assertions of the “Heart-Mini-Brain” hypothesis on the information contained in one website, HeartMath =  She also cites a book, The HeartMath Solution, authored by the founders of the website.  Dr Leaf does not offer any other support for her position other than that of HeartMath.  Indeed, when she states the same information in her new book as well, she still only quotes HeartMath.

So then, does HeartMath offer convincing evidence that the heart is really a mini-brain?  There seems to be a lot of science to go through on their site, but on further analysis, there are only a few genuine citations.  Many of their references are unpublished work or abstracts presented at conferences.  As evidence goes, it’s not very strong.

Other citations, such as “The Electricity of Touch: Detection and measurement of cardiac energy exchange between people” [254] aren’t scientific papers at all.  Even the authors admit it: “The research described here was not designed as a comprehensive, rigorous study to yield results to be subject to statistical analysis, and is not intended to be presented or evaluated as such a study … The results described in this paper are representative examples of the types of data that have been collected from numerous experiments conducted with many different subjects over several years’ time.”

There is nothing wrong with expressing your view or sharing your theory.  But despite the study’s disclaimer, HeartMath cites this paper as evidence for an energy connection between people: “This study represents one of the first successful attempts to directly measure an energy exchange between people, and provides a solid, testable theory to explain the observed effects of many healing modalities that are based upon the assumption that an energy exchange takes place.” [255]

So HeartMath are happy to use guesswork and opinion as the foundation for their theories, which in itself doesn’t prove them invalid, it just ruins their scientific credibility.

But to be thorough, lets still examine what Dr Leaf via HeartMath says about the heart as a little brain.  HeartMath believe that the heart has a “little brain” because:
> The heart has a network of 40,000 neurons within it, called sensory neurites, which detect circulating hormones, neurochemicals, and sense heart rate and blood pressure.
> The heart secretes “neurotransmitters” and other hormones, which have an effect on the brain, such as atrial natriuretic factor, and oxytocin.
> The heart communicates with the brain and the rest of the body through neurological, biophysical, biochemical and “energetic” (ie: electromagnetic) means [132, 255].

HeartMath states that, “The heart’s brain is an intricate network of several types of neurons, neurotransmitters, proteins and support cells like those found in the brain proper. Its elaborate circuitry enables it to act independently of the cranial brain – to learn, remember, and even feel and sense.” [132]

And, “More recently still, it was discovered that the heart also secretes oxytocin, commonly referred to as the ‘love’ or ‘bonding hormone.’ Beyond its well-known functions in childbirth and lactation, recent evidence indicates that this hormone is also involved in cognition, tolerance, adaptation, complex sexual and maternal behaviors as well as in the learning of social cues and the establishment of enduring pair bonds. Remarkably, concentrations of oxytocin in the heart are as high as those found in the brain.” [132]

So the “evidence” looks plausible on the surface, but when it’s considered in a broader biological context, the weaknesses of the theory start to appear.  For example, my heart may have 40,000 neurons, many of which are sensitive to circulating hormones, neurochemicals and which sense and feel, but then again, so does my rectum.  Does my rectum have a mini-brain as well?

Indeed, the entire gastrointestinal tract has more nerve cells within it than the entire central nervous system, and we are much more aware of sensations from our gut on a daily basis than we are of our heart.  The GIT also contains almost all of the “neurotransmitters” that are also found in the brain [220].  If anything, that would make the gastrointestinal tract a much better candidate for having a mini-brain, and some have even suggested it [256].  But most of our organs or our limbs have large, organized and highly functional neural networks, yet they don’t think, plan, or control other parts of our body.  Does the skin have a mini-brain too, or the uterus, or the spleen?  The answer is no.  Our brain does not delegate its work to other organs.  Doctors and scientists sometimes say that, “the gut has a mind of its own”, but they’re talking metaphorically, not literally.  Is the way to a man’s heart literally through his stomach?  Of course not.  And neither the gut, nor the heart, has a mini-brain.

HeartMath also state that the heart produces oxytocin, which then has an effect on the brain.  Actually, the heart has a large number of oxytocin receptors, proteins that receive the hormone signal.  Some oxytocin is produced by the heart itself [257] although the vast majority of the production of oxytocin is from the brain [258].  The heart is very sensitive to oxytocin signals because oxytocin causes the release of atrial natriuretic peptide (ANF) from the heart, which then acts to modulate blood pressure [257].  The oxytocin from the heart isn’t required for cognitive or emotional processing in the brain.

Then there is the claim that the electromagnetic signal generated by the heart influences the energy of every cell in the body.  The electrical signal from the heart can be picked up by specialised electrodes placed on the skin from as far away as the lower leg.  This measurement is performed thousands of times every day in doctors offices and hospitals worldwide.  It’s called the ECG (or the EKG in America).

ECG stands for electrocardiogram.  To perform an ECG, the patient lies on a bed, and highly sensitive electrodes are placed at standardised points on the limbs and on the chest.  The patient should lay still and breathe gently, and a ten second sample of the heart’s electrical current is recorded at all twelve “leads” simultaneously.

Each “lead” of the standard 12-lead ECG is actually a measurement of flow of electrical current between two of the electrodes placed on the skin.  Electrical current moving towards the positive terminal of the lead makes the line go up, and electrical current moving away from the positive terminal makes the line go down.  Each bump and wave of the ECG line represents the flow of electrical current within different parts of the heart within the cardiac cycle.

Most important for our discussion here, the height of the ECG wave, called the amplitude, is only about 1 to 2 millivolts [5: p137].  To give you an idea of how small that amount is, the standard AA sized alkaline battery is capable of producing 1.5 volts.  So in comparison, the ECG signal detectable at the skin is 1500 times smaller than a standard battery.  The signal from the heart is so delicate that it can only be detected by a machine with electrodes coated with high conductance gel, and a specialized electrical filter to reduce the background electrical noise produced by the muscles. 

Compared to all of the electrical noise generated by the body, the signal of the heart is small and soft, and is easily overwhelmed.  It’s like a single choirboy trying to sing Amazing Grace in the middle of a mosh-pit at a heavy metal concert.  Suggesting that the hearts electrical signal is able to influence the other cells and tissues in this chaos of electrical current are far-fetched.

Likewise, the magnetic signal of the heart is also extremely weak.  An MCG, the magnetic equivalent of the ECG, is measured in units of picoTeslas [259], or one trillionth of a Tesla.  To give some comparison, the Earth’s background geomagnetic field is around 50,000nT in the UK [260], while your average fridge magnet is 10 milliTesla [261], about one billion times stronger than the signal detectable from the heart.  To get a useful reading, the patient has to be locked in a tiny room that is magnetically shielded to avoid the noise of everyday electromagnetic signals.  Unshielded machines are available but require high-order gradiometers, synthetic gradiometers, integrated reduction devices and advanced post-processing to partially compensate for the background magnetic noise [259].  Again, muscles and other bioelectrical signals also generate magnetic fields, so the suggestion that a weak signal, easily swamped by the magnetic signals of the body and the environment, could somehow influence the rest of the body’s cells is hard to believe.

The “Still Small Voice” Comes From The Brain

So if the still small voice that Dr Leaf is referring to doesn’t come from the heart, then where does it come from? 

Dr Leaf states, “Your heart is in constant communication with your brain and the rest of your body, checking the accuracy and integrity of your thought life.  As you are about to make a decision, your heart pops in a quiet word of advice ...” [1: p62]  Is she referring to the moral conscience, evaluative judgement, or operational prudence (ie: making smart decisions)?  Either way, the foundations for all three possibilities are found in the frontal parts of the brain.

Mendez summarised the scientific evidence on the moral conscience, “This neurobiological evidence points to an automatic, emotionally-mediated moral network that is centered in the ventromedial prefrontal cortex (VMPFC), particularly in the right hemisphere.” [262]

Evaluative judgements (for example: “I like One Direction = Yes/No”) are the assessment of an external or internal stimulus on an internal scale related to the person’s value system (preferences, norms, aesthetic values, etc).  These are largely processed within the anterior frontomedian cortex [263].

In terms of making appropriate decisions, the rewards value for a choice is processed in the left ventro-medial prefrontal cortex, and the striatum [264].  Feeling positive about a decision is the result of the dopamine neurotransmitter, which is one of the main neurotransmitters used in the connections between the nucleus accumbens, striatum and the pre-frontal cortex.  When dopamine pre-cursors have been depleted in the body, the rewarding component of decision-making is lost [265]

So the scientific consensus is that the pre-frontal cortex and dopamine are responsible for the still small voice that helps us with decisions, rather than the heart.


Dr Leaf, via HeartMath, stated that it was Atrial Natriuretic Factor, or ANF for short, that was responsible for the feeling of peace after “listening to your heart”, rather than dopamine.

ANF originally got its name from its origin (it’s produced by the walls of the atria, the top two chambers of the heart) and for its action (natriuretic means that it acts to excrete sodium).  ANF is released from the cardiac muscle cells in response to excessive stretch of the wall of the atria, usually in response to an increase in the volume of blood in the body [5: p376] (although adrenaline can also trigger its release [266]).  It’s not particularly significant compared to other mechanisms for controlling blood volume, because a large infusion of ANF only causes a small change in blood volume, which lasts for about 24 hours before being compensated for by other physiological mechanisms [5: p376].

Over the decades since it was first described, further study showed that there were four different forms of ANF: short protein chains called peptides, found in different parts of the body, such as the heart, brain, kidneys and blood vessels.  Together they work to dilate the blood vessels to decrease blood pressure, enhance the salt and water excretion by the kidneys, and reduce thirst and the desire for salt, which decreases the overall blood volume [266].  It also blocks the background activity of the sympathetic nervous system (the fight-or-flight system) on the blood vessels which allows them to dilate, assisting in the reduction of blood pressure [267].  The combination of effects helps the body control the volume of blood the heart is required to push around, ensuring it’s not overloaded.

But it’s the effect that ANP has on the sympathetic nervous system that has excited some scientists about the possible effect of ANP on anxiety.  In small human trials, panic attacks were induced using a digestive hormone called CCK4, but pre-treatment with ANP reduced this effect, although it was less effective in subjects with a known diagnosis of panic disorder [268].  A similar study was performed, again in the lab, with a very small number of patients, but this time the ANP was induced by 30 minutes of aerobic exercise.  This study showed a similar result, that exercise-induced increases in ANP also reduced CCK4-induced panic attacks [269].

This sounds like a win for ANP, and certainly, there is a plausible mechanism through which ANP may reduce panic symptoms, through the reduction of the sympathetic tone.  But while it’s fine in theory, there are a number of difficulties in the real life application of the findings.

Firstly, the numbers used in the trials were very small, with only two published studies on the subject that I could find, one with 18 subjects [268], and the other with only 10 [269].  The statistical power of such small cohorts means that they’re very hard to extrapolate. 

Secondly, the dose of the CCK used to induce the panic attacks and the dose of the ANP used to truncate them, were extremely high compared to normal levels.  For example, the dose of CCK in the study by Wiedemann [268] was 19,000 times greater than the normal physiological levels of CCK and still about 3,000 times greater at the peak concentration of CCK after a fatty meal.  Similarly, the dose of ANP used was about 1000 times greater than normal physiological levels.

Just as we don’t suffer from panic attacks every time we have a meal, it’s highly unlikely that ANP is ever at a physiological level high enough to offer meaningful anxiety reduction in a real life setting.  For example, heart failure causes huge amounts of ANP to be released [5: p261].  Despite disagreement by some authors [270] the vast majority of patients with CCF have high anxiety [271], despite their huge amounts of circulating ANP.

So while ANP has very interesting effects on anxiety in a laboratory setting, it’s not associated with feelings of peace in real life.  Its function is to help regulate blood volume.  It is not a cognitive checkpoint.

The Heart-As-A-Mini-Brain concept – Everything old is new again

In conclusion, there is no tangible scientific evidence that the heart acts as anything other than a heart.  The heart is not a mini-brain any more than your spleen, liver or uterus is a mini-brain.  In fact, if Dr Leaf’s criteria for a mini-brain were strictly followed, the intestines make for a much better candidate for a mini-brain than the heart ever would.

But the main point here is that the notion that the heart (or any other organ) is in any way responsible for cognitive functioning was disproven two millennia ago.  To seriously advocate that the heart acts to guide thinking is no different than suggesting a hysterical woman has a migrating uterus.  It’s harking back to the dark ages, and is completely at odds with modern scientific knowledge.