Does the Polygraph Measure Your Heart? Not at this Rate

Following the Christmas and New Year holiday it occurs to me that the heart is probably very busy organ over this period.

The joy of family reunions, the tension of family arguments, the excitement of presents, the food coma from eating so much, the abnormal amounts of drinking, a New Years Eve kiss, all of these things affecting your heart in someway.

Your heart is important (obviously), and there are a number of reasons why the polygraph measures your heart. Let me expand…

In a nutshell, your heart is really important, but we know that, so why does the polygraph measure your heart?

If you have read either of my blogs about the polygraph and sweating, or the polygraph and breathing, you will know that I paid particular focus on the autonomic nervous system.


Are you interested in learning more about what the polygraph measures and why? Please have a look at some of our other blogs.


The 2 main systems that regulate the cardiovascular system (your heart) are the Autonomic nervous System (ANS) and the renin-angiotensin system (RAAS). Don’t worry about the RAAS, I wont mention that again.

diagrams of the brain

The brain and body connection is fascinating but very complicated.

For those of you that haven’t read the blogs, I would recommend you have a quick look as I’m breaking down each component of the polygraph, but I will give you a brief run down of the ANS.

The ANS is split into 3 parts (the 3rd part won’t be mentioned), that includes the:

  • Sympathetic Nervous System (S/ANS) and
  • Parasympathetic Nervous system (P/ANS)

all of which is out of our control.

The ANS is responsible for the regulation of our bodies temperature, digestion, heart rate and excretion amongst others.

You can’t control any aspect of digestion once that Christmas dinner enters your stomach and you certainly con’t control your body heat or heart rate rising for that New Years kiss.

The Sympathetic part of the ANS gets us ready for action, the phrase ‘fight or flight’ to some people. Whereas the Parasympathetic portion does the exact opposite and brings up back to normal and maintains homeostasis.

Story Time

road sign

Imagine yourself on a road – perhaps a story road.

Imagine you’re on a pavement somewhere, maybe in your favourite city, or the road outside your house, you want to cross the road. Close your eyes and just picture yourself walking, what sounds can you hear? Any smells? Are the smells familiar to you? Are you aware of the rhythm of your breathing?

You have a quick glance and you can’t see anything coming and you can’t hear anything but you are aware of phone because it’s vibrating in your hand. You step out into the road.

Suddenly you hear something loud. it sounds fast. It’s dangerous and you’re trying to work out what it is. You look up from your phone, see a car about 5 metres away! You panic! Somewhere in your head a memory is popping up to say that a moving car is dangerous.

What do you do? You know if you stay still it’s going to hit you but it’s so close, will you be able to move in time? Somehow the car misses you. Phew!

It is estimated that the ‘fight or flight’ response takes ‘250ths of a second’, that’s pretty darn quick.

As soon as your brain registered a moving car heading towards you, it took autonomy of your body, decided you were in danger and needed to move, activated the necessary hormones and muscles and got you out the way.

The point I want you to think of is how you feel after. You realise that you’re seriously pumped up and wired. You’re breathing faster, heart is pumping, little bit sweaty maybe. All of which was activated without your control. That’s the autonomic nervous system for you, specifically the sympathetic part.

So Why Does The Polygraph Measure Your Heart?

The polygraph is sometimes known as a psycho-physiological detection of deception. Ignore the ‘detection of deception’ part and let’s focus on the ‘psycho-physiological’.

Definition of Psycho-physiology

Definition of Psycho-physiology

In a nutshell, this is the relationship between the brain and the body and how they effect each other.

There are lots of theories that discuss why the polygraph works and why and what we react to all based on current scientific research.

These include things such as Orienting and Defensive Responses, Emotion (including fear and nerves), Cognition and Behavioural Conditioning etc. all of these are worth exploring in further blogs which I will get around to soon – I promise.

Definition of the Orienting response

Definition of the Orienting response which is one of the phenomena that effect your heart rate

But all of these can be looked at from a psycho-physiological viewpoint i.e. these things start in our brain and have an effect on our body and vice versa.

Orienting Theory and the Heart

Without going into too much detail now about what Orienting Theory (OR) is, it basically means if something enters our awareness and we find it new, significant or novel we react to it.

A researcher called Sokolov suggested that if there is a mismatch in the information coming in e.g. a polygraph question about a certain subject, and the information already in your memory e.g. about an incident, there will be an OR.

In other words, if you are asked a question about a topic that you have to respond to with a lie, there is a mismatch so there is likely to be a reaction.

He called this a ‘novelty stimuli’.

This then has an effect on our body.

For our heart rate, research shows it causes a fall in heart rate and increased systemic blood pressure (systemic is the blood pressure in the main arteries of your body). This is what we measure in polygraph.

Emotion, Cognition, Behaviour and Heart Rate

A Stress ball

Stressed out? A small ball to squeeze helps

We all know the effect stress has on our blood pressure. It would be silly to try and suggest nobody would be either stressed and/or nervous and/or upset and/or angry during a polygraph test. Whether you have something to hide or not.

That’s normal and natural and that is not something that we are bothered about as polygraph examiners. Our job is to ensure the test runs as effectively and accurately as possible and to make you aware of everything that happens.

To try and take some of the stress and nerves out.


I have written a blog about the role of an examiner and one of those roles is to guide a person through a test. If you’re interested in reading more please have a look at that blog.


There is research to suggest that our heart rate is connected to our emotion in many ways, one of those ways suggested is: ‘with novel or “alerting” stimuli‘.

You’re probably thinking this is the same as as the reaction described for an Orienting Response. Well yes it’s very similar, because the whole point of the OR is we process whatever it is that has caught our attention and compare it to previously held memories to help us identify it.

A Link Between Emotion and Memory

I would suggest, with those memories comes an emotion. If you think of something, you don’t just recall a cold image, it comes with a feeling: sad, happy, confusion, anger – whatever it is, they are connected to the memory.

The effect on our body? The same as an OR: decreased heart rate and increase blood pressure.

There are also experiments to show that our heart rate is affected by our concentration. What I mean is that when we are thinking hard, it can effect our heart rate and blood pressure. This is known as cognitive load.

Another reason why a polygraph measure your heart rate.

Behavioural Conditioning and Heart Rate

Firstly, there is a really good summary here of the two types of conditioning that are talked about by psychologists. It’s worth a read just because it’s interesting.

A snake in a palm

Humans are easily conditioned to fear snakes, no matter what their size.

Basically though, conditioning is our ability to learn and adapt and change our behaviour to certain stimuli to behaviour which suits that stimuli the best.

We might adapt to be naturally fearful of something e.g. human beings seem to be very easily conditioned to have a fear of snakes according to the Human Evolution Blog. Or we might learn that when a bell is rung, it means food so we start to salivate i.e. Pavlov’s Dogs.

How Does Behavioural Conditioning Relate to Polygraph?

The point about behavioural conditioning is that we have been told, raised and taught that lying is bad and that we shouldn’t do it so our behaviour adapts and when we do lie, we know our behaviour is wrong.

Small or white lies are known as a social lubricant, help the day go a bit smoother, everyone does it. What I am talking about is the big stuff, the hurtful lies to loved ones, to bosses, lies that hide serious misgivings from our past that would affect a job.

The Feeling of Lying

When we tell those kind of lies (which most of us have) we usually get that feeling in our stomach, hearts, chest, all over our body in fact, that makes us want to run away, kind of catches our breath and heart starts pumping.

You may have heard the terms ‘fight or flight’, most people know this as the extreme evolutionary conditioning of survival. When we are threatened, we usually decide to run or fight, usually without our conscious selves in control.

Fight or Flight & Perhaps a Freeze?

A list of the reactions in your body when a 'fight or flight' response occurs

A list of the reactions in your body when a ‘fight or flight’ response occurs

This list is from Nottingham University and lists all the changes that happen in our body when a fight or flight response occurs.

I would argue that in this day and age our physical survival isn’t necessarily under threat, but our social position and survival could be, more of a mental threat. Along with our ego and self esteem, our relationships and our livelihood.

It is unlikely that a full ‘fight or flight’ response will be elicited; however, a slight rephrase of that term to: ‘the thinking persons fight or flight’ (catchy I know) seems to capture what might be happening during a polygraph test.

Another more commonly seen phrase is ‘fight flight or freeze’. In any case, both phrases describe the act of assessing the threat (physical or mental) to gather more information about it. It also allows our Anterior Prefrontal Cortex (read on for the role this plays) the time to construct a lie.

However, the response in our body is still the same as the picture shown above.

a person being pointed at

There are many repercussions if we are caught out lying.

Because we have been conditioned not to lie, when we do, we feel bad. Moreover, as we grow up we realise the mental threat from being discovered as a liar: embarrassment, shame, isolation, judgement.

When we are asked a question about a significant issue, if we have to lie to in order to maintain our social and personal relationships, we are faced with a mental threat so we freeze. We start constructing a lie and our bodies begin to react.

The polygraph measures your heart because that is one of the parts of your body to react.

Your Brain Should Hurt After a Lie

On a side note, telling a lie is cognitively demanding. It starts in our frontal lobe which is responsible for higher thinking, evil plans, personality, emotion and problem solving amongst others.

There is a suggestion that the frontal lobe (in particular the Anterior Prefrontal Cortex) is heavily involved in deception and the construction of a lie. To construct a lie often takes effort, time and a lot of neurotransmitters firing to access the different parts of the brain needed to construct it.

I won’t go into too much detail because I’m digressing slightly.

How Does The Polygraph Measure Your Heart?

This is possibly the simplest part of the entire polygraph.

A standard blood pressure cuff.

A standard blood pressure cuff.

We use a standard blood pressure cuff that you will see in any doctor’s room. Goes around your upper arm, lower arm, or lower leg depending on wherever is most stable.

This measures relative changes in your blood pressure during the test and gives the examiner an image showing our systolic (the top number of your blood pressure) and diastolic (the bottom number of your blood pressure).

We don’t see the numbers though, so we can’t give you a health check at the same time unfortunately.


If you found this interesting, please share it with others or like it. My goal is to educate people about the polygraph. Your help is appreciated.

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