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LECTURE – 3
DR. ZAHOOR ALI SHAIKH
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CARDIAC CYCLE

Cardiac events occurring during one
beat (systole & diastole) are repeated
during the next beat

Cardiac cycle time : 0.8 second when
heart rate is 75 beats per minute.
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CARDIAC CYCLE

Atria and Ventricle go through separate
cycles of systole and diastole.

When we use the term Systole and
Diastole, we refer to ventricles, until
unless specified for atria.
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We will discuss mechanical & electrical
changes during Cardiac Cycle
Mechanical changes:
1. Phases of cardiac cycle
2. Pressure changes during cardiac cycle
3. Volume changes during cardiac cycle
4. Heart sounds
Electrical Changes
5. Electrocardiogram (ECG)
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ECG
 ECG ( Electrocardiogram) – These electrical events can be
recorded by putting electrodes on the surface of body
 P wave – Atrial depolarization
 QRS - Ventricular Depolarization
 T wave – Ventricular Repolarization
We will discuss
ECG in detail in
coming lectures.
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MECHANICAL CHANGES
1. PHASES OF CARDIAC CYCLE
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PHASES OF CARDIAC CYCLE
Atrial systole: 0.1 second
 Atrial diastole : 0.7 seconds



Ventricular systole : 0.3 seconds
Ventricular diastole : 0.5 seconds
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CARDIAC CYCLE
0.7 Sec.
0.1 sec.
AD
AS
Atrial Cycle (0.8 Sec.)
0.3Sec.
0.5 sec.
VS
VD
Ventricular Cycle (0.8 Sec.)
AS – Atrial Systole;
AD – Atrial Diastole ;
VS – Ventricular systole;
VD – Ventricular diastole
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Ventricular events

1.
2.
Ventricular systole
Isovolumetric contraction
Ejection phase
 Rapid ejection
 Slow ejection

Protodiastolic phase

Ventricular Diastole
1.
2.
Isovolumetric relaxation phase
Filling phase
 Rapid filling
 Slow filling
 Last rapid filling
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Ventricular events
Ventricular systole
1. Isovolumetric Contraction
When blood has come from Atria into
the ventricle, ventricle will start
contracting, when pressure increases in
ventricle than atria, AV valves close.
 This phase of ventricular contraction
when all valves are closed is called
ISOVOLUMETRIC CONTRACTION.

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Ventricular systole

During Isovolumetric Contraction,
volume remains same, but pressure in
the ventricle must continue to increase
till it exceeds aortic pressure.
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Ventricular systole
2. Ejection Phase
 When ventricular pressure increases,
semi-lunar valve [aortic and pulmonary
valves] will open and blood will flow into
aorta and pulmonary artery. This is
Ejection Phase [pumping of blood out].
 Ejection is rapid first and then slow.
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Protodiastolic phase
Once ventricle muscle is fully
contracted, than it will relax and
ventricular pressure will drop rapidly.
 When ventricles are relaxing, but aortic
and pulmonary valves have not closed
yet, this period is called Protodiastole.
 It lasts for 0.04 sec.
 It ends when aortic and pulmonary valve
close.

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Ventricular Diastole
1.
Isovolumetric Relaxation
During diastole, When ventricular
pressure falls below the Aortic pressure,
aortic valve closes, and AV valves are
not open yet , ventricle is close cavity
with all valves closed. This phase is
called Isovolumetric Relaxation (means
volume remains same but pressure is
decreasing).
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Ventricular Diastole
2. Filling phase




When ventricular pressure falls below the atrial pressure, AV
valve open and blood moves rapidly from the atria into the
ventricles – first rapid filling phase [causes 3rd heart sound].
Then blood comes slowly – slow filling phase.
Then atria contract for 0.1sec and blood comes fast into the
ventricle – last rapid filling phase [causes 4th heart sound].
NOTE
Last rapid filling phase is due to atrial systole and contributes
to 20-30% of ventricular filling.
After atrial systole, cardiac cycle will re-start.
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Relation Of Heart Sounds With Phases Of
Cardiac Cycle
0.7 Sec.
0.1 sec.
AD
AS
VS
VD
0.3Sec.
0.5 sec.
1 st Heart Sound
2 nd Heart Sound
3 rd Heart Sound
4 th Heart Sound
HEART SOUNDS
AS – Atrial Systole;
AD – Atrial Diastole ;
VS – Ventricular systole;
VD – Ventricular diastole
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Tachycardia, Effect on Cardiac
Cycle
During Tachycardia, when heart rate is
increased, both systole and diastole
time decreases.
 Diastole length (time) is shortened much
more than systole length. Therefore it
reduces the time for ventricular
relaxation and filling.

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2. PRESSURE CHANGES DURING CARDIAC
CYCLE
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Rt- Atrium = 0-7mm Hg.
Lt- Atrium = 2-10 mm Hg.
Rt – Ventricle = 25 / 6(2-8) mm Hg.
Lt – ventricle = 120 / 8(2-10) mm Hg.
Aorta = 120 / 80 mm Hg.
Pul. Artery = 25 / 10 mm Hg.
Pressure changes during cardiac cycle
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
Draw pressure curve for Lt.ventricle, Aorta &
Lt. Atrium

Draw pressure curve for Rt. Ventricle &
Pul. Artery.
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Events of cardiac cycle showing pressure changes in left ventricle,
aortic pressure, atrial pressure, ECG & phonocardiogram
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pressure curves for Rt. ventricle. & Pulmonary Artery
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3. VOLUME CHANGES DURING
CARDIAC CYCLE
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
Define Stroke Volume (SV)

Define End Diastolic Volume (EDV)

Define End Systolic Volume (ESV)

Define Ejection Fraction (EF)
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
Stroke Volume: It is a volume of blood pumped out
by each ventricle per beat. It is about 70 - 80 ml.
Stroke volume (SV) = EDV – ESV

End Diastolic Volume: Volume of blood in each
ventricle at the end of diastole.
It is about 120 – 130 ml.

End Systolic Volume: Volume of blood in each
ventricle at the end of Systole. It is about 50 to 60 ml
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Volume changes during cardiac cycle
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Events of cardiac cycle showing left ventricular pressure, volume
changes, & phonocardiogram
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
Ejection fraction (EF) is the percentage of
ventricular end diastolic volume (EDV) which
is ejected with each stroke.
EF =
SV (EDV – ESV)
X 100
EDV
75
X 100 = 62.5%
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Normal ejection fraction is about 60 – 65 %.
Ejection fraction is good index of ventricular function.
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Heart Sounds

We will discuss Heart Sounds in next
lecture.
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What You Should Know From This
Lecture
Cardiac Cycle – Definition
 Phases of Cardiac Cycle
 Pressure Changes
 Volume Changes
 Period of Systole & Diastole During
Tachycardia
 Relationship of Heart sounds with
Cardiac Cycle

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Thank you
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