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- (Narrator) To continue
dealing with the heart

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we have to talk about the cardiac cycle.

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How the heart contracts and relaxes.

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Because your heart never
really takes a break.

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But it must take a short break.

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So even though you're heart is beating

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60, 70, maybe even 80 times a minute,

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you still need to make
sure that the heart beats,

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that the muscles can relax for a moment.

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Not long, but a very quick relaxation.

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So we'll start with the atrial systole.

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Systole is a term referred to when

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the muscle of the heart is contracting.

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So in atrial systole, both atria contract

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pushing blood down into the ventricles,

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helping to fill the ventricles up.

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Well if blood's going from the
atria down to the ventricle,

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the AV valves must be open.

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Now both the pulmonary and aortic

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semilunar valves are closed.

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The blood is not leaving the heart yet.

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It's just accumulating
inside the ventricle.

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In ventricular systole,

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well that means we have contractions.

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Both ventricles contract.

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Now the ventricles
contract, they're trying to

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generate force to push the
blood out of the heart.

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Well they're pushing it out of the heart

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that means the aortic and pulmonary

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semilunar are opened,
allowing the blood to leave.

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But the atrial ventricular,
or the AV valves, are closed.

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They're preventing the backflow of blood

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back up into the atria.

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Diastole, that's relaxation.

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Both you'll have atrial diastole
and ventricular diastole.

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When this occurs, the
semilunar valves are closed.

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All the ventricles and
all the atria are relaxed,

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slowly, passively filling with blood.

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So here we show the movement
of blood to the heart.

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First off, we'll start with
systole, that's contraction.

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You notice it only starts
in about point one seconds.

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So there's not very much
time during atrial systole.

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So this is when the atria contract,

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pushing blood into the ventricle.

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Then we go into ventricular systole.

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This lasts about point
three seconds, or so.

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At this point, the
ventricles are contracting,

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pushing blood out to the semilunar valves,

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out through the aortic
and pulmonary trunk.

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As you can see both the right and left

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AV valves are closed, preventing backflow.

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Then we end up with
diastole, the relaxation.

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Both atria and ventricles relax

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allowing for the blood to flow

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passively down in the ventricles.

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You have to say, hold on...

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Point one plus point
three plus point four,

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that only equals point eight seconds.

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That's as long as normal heart beats.

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Because the average heart
beat's up in the 70s somewhere.

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Some people are in the 80s,
some people are in the 60s.

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Sure, no problem.

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But if you average everyone
out, it's about in the 70s.

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So that means that point eight seconds

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is how long each one of
those beats would take

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to get into the 70s per minute.

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I'm sure you've all heard of this

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lub-dub, lub-dub, lub-dub.
It's the heart sound.

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It's the sound of the heart
closing the heart valves.

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The first sound, the quote lub sound

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is when both the AV valves close.

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Now these AV valves are going to close

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when the ventricles are contracting.

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When the ventricles are in systole.

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Well the second sound, the dub sound

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is when both semilunar valves close.

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Both the pulmonary and aortic snap shut.

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That can only happen once the
ventricles stop contracting.

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So this lub-dub sound is the
AV opening and the closing.

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The dub is the semilunar closing.

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So it's constant back and forth.

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Which valve is open?
Which valve is closed?

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So the first ones to close are the AV,

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making sure the blood moves forward.

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The second ones to
close are the semilunar,

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preventing blood from
coming back into the heart.

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But sometimes we end up with
problems, heart murmurs.

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Now heart murmurs are caused

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when the blood flow is disrupted.

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It could be disturbed somehow,

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it might be a defective valve.

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It might be the valves
are not formed properly.

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There might not be a lining.

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They might not be closed...

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You get the idea. Something
is wrong with the valve.

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So if blood flow is being
disturbed, it's being disrupted,

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it's creating an extra sound.
That is your heart murmur

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So how does the heart beat?

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Well we have this whole
entire conduction system.

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Your heart has it's own intrinsic,

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or within, electrical system.

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The first piece of this five
part puzzle is the SA node.

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The SA node is your cardiac pacemaker.

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It's what starts the heartbeat.

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What's kind of weird is
this works by itself.

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So you can actually be holding a heart

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that was just removed from an organism.

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That heart would keep
beating for a short time.

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The SA node just keeps firing.

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It eventually stopped beating

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because of a lack of nutrients,

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a lack of particles to feed it.

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The AV node?

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Well, the AV node is
simply a relay station.

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It's meant to take the
signal from the SA node

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and pass it down the
line to the AV bundle.

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Now the AV bundle is going
to be receiving the signal

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and carrying it down to the
ventricles, the Purkinje fibers.

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So we have our SA node, AV node,

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AV bundle and Purkinje fibers.

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But you're thinking,
hold on. He said five.

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There is a fifth one.

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It goes up where the
AV bundle is, as well.

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So between the AV node
and the Purkinje fibers

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you actually have two different components

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that help to relay the information.

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So here we go.

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We start with the SA
node, the sinoatrial node.

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Send signals to both atria.

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Then the AV node, ventricles carry

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the information down to the AV bundle.

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Then here's the new one, bundle branches.

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So the AV node, the bundle branches

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are carrying information
down towards the ventricles

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where the Purkinje fibers
are going to contract.

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Purkinje fibers are a stimulating
contraction of the muscle

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to cause the blood to
leave the ventricles.

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To be able to look at
these electrical impulses

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we look at an electrocardiogram.

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An electrocardiogram, or ECG,

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a lot of times more
commonly known as an EKG,

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is meant to track the electrical
activity of the heart.

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To track when the SA node fires

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and caused a stimulation, a contraction.

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Now the average healthy individual

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has a pretty typical pattern to their ECG.

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They have three main features

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called a P wave, QRS complex, and T wave.

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The P wave is when the
atria are being stimulated,

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the atria are contracting.

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QRS complex, now that's talking about

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when the ventricles are being stimulated,

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when the ventricles are contracting.

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And the T wave is the end
of electrical activity.

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It's the point where the heart needs

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to rest momentarily, before
the next P wave occurs.

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Now these EKGs can basically detect

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a few different problems;

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things like arrhythmias,
ventricular fibrillation.

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So you can tell what's going on

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and give the medical personnel a

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better idea of how to help the individual.

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So here's how an EKG runs.
You can see one up top.

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A lot of times you have
all these different wires

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all over the heart, as well
on the arms and the legs

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trying to measure an electrical signal.

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Letter B you can see is the normal ECG.

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You have a little P
wave, then a QRS spike,

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and a little T wave.

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Another P wave, QRS and T wave.

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Now that's typical.

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But the one on the bottom,
we've got a little problem here.

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That's called ventricular fibrillation.

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If you notice, it does not come

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close to matching the normal one.

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In ventricular
fibrillation, the ventricles

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are just rapidly contracting.
On, off. On, off. On, off.

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In no real pattern.

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In ventricular fibrillation
that's really dangerous.

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You better get yourself to
a hospital very quickly.

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Otherwise this could potentially kill you.

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Because the heart, the
ventricles specifically,

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are beating erratically.

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The blood is not adequately being sent

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to the rest of the
body, impairing function

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of all the rest of the organs.

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So normal EKG, those
typical blips you see there.

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But one example of a problem
is ventricular fibrillation.