Introduction to the Heart’s Electrical System

Stepful

Mar 08, 2026

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2 min read

YouTube video ID: w6QMJ3Vb5dY

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The heart contains an internal electrical system that makes heart cells conduct electricity and start each beat. This conductivity creates the pulse that we count as beats per minute (BPM). The electrical activity also determines the heart rate, which is simply the number of beats that occur in one minute.

Measuring Heart Rate

To measure a regular, strong pulse, place your fingers on a pulse point, count the beats for 30 seconds, and multiply by two. If the pulse feels thready or irregular, count for a full 60 seconds to obtain an accurate number. For most adults, a normal resting heart rate falls between 60 and 100 BPM. When exercising for fat burning, aim for a heart rate that is roughly double the resting value—for example, a resting rate of 60 BPM corresponds to an exercising target of about 120 BPM.

Heart Rhythm and the Electrical Pathway

Heart rhythm describes the synchronized pumping action that moves blood throughout the body. An electrocardiogram (ECG or EKG) records the heart’s electrical conductivity and reveals the rhythm. The sinoatrial (SA) node, located in the atrium, acts as the body’s natural pacemaker by generating the initial impulse. If the SA node fails, the atrioventricular (AV) node in the ventricles serves as a backup pacemaker. The impulse travels from the SA node (or AV node) through the Bundle of His, then the Bundle Branches, and finally the Purkinje fibers, causing the ventricles to contract. This coordinated electrical flow completes one cardiac cycle. An impulse that originates from the AV node instead of the SA node can produce abnormal patterns on an ECG.

Cardiac Cycle Phases and Blood Pressure

A cardiac cycle is equivalent to one heartbeat and consists of two main phases. Systole is the contraction phase when the heart pumps blood out; it corresponds to the top (higher) number in a blood pressure reading. Diastole is the relaxation and refilling phase; it matches the bottom (lower) number in a blood pressure reading.

Implications of Heart Strain

When the heart works excessively, cells become damaged, or blockages develop, the systolic blood‑pressure number can rise, leading to high blood pressure. Chronic overwork may cause the heart to enlarge, increasing the risk of a heart attack. Monitoring heart rate, rhythm, and blood pressure helps identify these stressors early.

Takeaways

The heart’s internal electrical system triggers each heartbeat and determines the beats‑per‑minute rate.
A regular pulse is measured by counting 30 seconds and doubling, while a thready pulse requires a full 60‑second count.
The SA node acts as the natural pacemaker, with the AV node serving as a backup if the SA node fails.
Systole and diastole represent the contraction and relaxation phases of the cardiac cycle and correspond to the top and bottom blood‑pressure numbers.
Overworking the heart or damaged cells can raise systolic pressure, enlarge the heart, and increase the risk of a heart attack.

Frequently Asked Questions

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Helpful resources related to this video

If you want to practice or explore the concepts discussed in the video, these commonly used tools may help.

Heart Rate Monitor Recommended

A heart rate monitor lets you track beats per minute accurately, helping you stay within normal resting ranges and target exercise zones.

Amazon →

Blood Pressure Cuff

A blood pressure cuff measures systolic and diastolic numbers, indicating how well the heart handles strain and detecting high blood pressure early.

Amazon →

Ecg Machine

An ECG machine records the heart’s electrical activity, allowing you to observe rhythm and identify any abnormalities in the conduction pathway.

Amazon →

Cardiology Textbook

A cardiology textbook provides detailed explanations of heart anatomy, electrical pathways, and the mechanisms behind the cardiac cycle.

Amazon →

Links may be affiliate links. We only include resources that are genuinely relevant to the topic.

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Full Transcript YouTube

within your heart you have what's called
an electrical system this is the
electrical conductivity that's happening
within your heart cells it triggers the
heart cells to initiate that beat or the
pulse that we were practicing and
measuring in our past lesson
it's called a heart rate and the heart
rate is what gives us our beats per
minute
an average adult beat per minute or
pulse would be anywhere from 60 to 100
beats per minute meaning that if we were
to obtain a patient's pulse remember we
have two ways we can do this if it's a
nice regular strong pulse we can pulsate
that pulse for 30 seconds multiply that
number by two that would give us our
results
if it's a thready inconsistent pulse
hard to feel then we're going to palpate
that pulse for a full one minute and
we're going to document that number as
what we have no additional math required
there in any case where we'd like for
our patients to fall in normal range
would be anywhere from 60 beats to 100
beats per minute and that's at rest
meaning no exercise nothing intense
happening just at rest
uh if you want to know where your
exercising rate should be it should be
double what your resting heart rate is
so if your resting heart rate Falls at a
60 you're exercising you want to learn
how to burn fat then you should be
doubling that number at about 120.
so we have the term heart rate which is
our beats per minute and then we also
have the term heart rhythm and the heart
rhythm is the synchronized action in
which your heart is pumping it's pumping
the blood through the valves through the
chambers of the heart we're able to
regulate that on what's called an ECG or
an EKG
electrocardiogram in the electrical
conductivity of the heart it all starts
with what's called this SA node or
sinoatrio node
cyanoatrial node is located in the
atrium of the heart what it does
involuntarily is it creates the impulse
for the heart cells to contract and
relax as that happens what's occurring
is one cardiac cycle it cannot be done
without the electrical impulse that is
said throughout the cardiac cells so the
SA node is referred to as the body's
natural pacemaker of the heart
there are circumstances where that essay
note could be faulty uh and when that
does occur those will be our patients
that have pacemakers put in place the
pacemaker could be the primary action of
the cardiac cycle or it could be put in
place as a backup method to help an
individual who may have an essay note
that tends to not beat on a regular
basis
now going down in the electrical system
of the heart the next system we have is
called the AV node
typically what happens is if the sa note
the sinoatria note is defective for
whatever reason the AV node is our
backup method it sits in the ventricles
so if that first impulse in the atrium
does not trigger then we can expect to
see the trigger occur within the AV node
as that trigger in the AV node uh sends
out its impulses it's then going to
speak to the ventricles allowing the
ventricles to work its part throughout
the cardiac cycle and hopefully get the
heart rhythm back on track
because the initial occurrence happened
in the AV node if we were to do a
readout on this on an EKG machine we
could expect to see some abnormalities
in the patient's Rhythm and that is
because the initial conductivity of the
heart should be happening within the
atrium in the SA node AV node is simply
a backup
in any case whether it occurs in the SA
node or the AV node as it sends out that
electrical pulse maker um it's going to
send out that activity all throughout
the heart and the entire heart Embraces
that it sends signals through What's
called the bundle of His
to the bundle of branches and then the
purkinje fibers
all of that works hand in hand and
allowing the contraction and the
relaxation of the heart uh that equates
to one heartbeat or one what we call
cardiac cycle
now here is where the sinoatrial node is
located here in the atrium and moving
our way down we have the AV node or the
atrial ventricular note this would be
the backup method
once the natural pacemaker sends out
that cardiac trigger it's going to send
the impulse out to the cardiac cells it
tells the cells that now they need to
contract and they need to relax that's
what's occurring here throughout the
heart
and what we see is the one cardiac cycle
which is really just a heartbeat the
bundle of His located in between the two
ventricles
also receives the impulse or the
electrical charge and it sends it out
even further through the purkinje fibers
the purkinje fibers then receive further
communication and that signals those
ventricles to contract
and allow for the conductivity to
continue which again is one cardiac
cycle
two terms here within the cardiac cycle
you have systole or diastolic or
systolic or diastolic
just remembering from when we were
learning blood pressure remember
systolic would be our top number
diastolic would be our bottom number in
acquiring a patient's blood pressure
reading
and what we're monitoring is the
Contracting and the relaxation of the
heart
so systolic is going to be when the
heart is Contracting our top number
diastolic when the heart is refilling
it's a period of relaxation and the
heart is filling again with the blood
and so if you have a heart that's
overworked or you've got cardiac cells
that are damaged then what we're going
to expect to see another thing with
blockage within the heart we're going to
expect to see a higher systolic number
high blood pressure the heart is working
harder it's pumping it's Contracting
it's relaxing in higher numbers it's
working harder to do the job to get that
blood to go through those valves as it
should not what we want on a regular
basis our heart has the ability to
sustain but we don't want it to overwork
day to day this could cause conditions
of an enlarged heart and overworked
heart and could definitely put a patient
at risk for a heart attack