‫بسم هللا الرحمن الرحيم‬
Cardiac cycle
Lecture by
Dr.Mohammed Sharique Ahmed Quadri
Assistant professor ,Physiology
Objectives
• To know about different phases of cardiac
cycle
• To understand the volume, pressure and
electrical changes during the cardiac cycle
• To emphasize the inter-relationship between all
these changes
• To know the event that leads to the heart
sounds
• Recognize the relation ship of heart sounds
with events of cardiac cycle
Cardiac cycle
 Cardiac events that occur from beginning of one
heart beat to beginning of next are called the
cardiac cycle .
 Cardiac cycle consist of alternate period of systole
(contraction/emptying)& diastole(relaxation/filling)
 Contraction results from spread of excitation across
the heart & relaxation follows subsequent
repolarisation of cardiac musculature.
CARDIAC CYCLE
• Cardiac cycle time : 0.8 second when heart rate is
75 beats per minute.
• 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.
4
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
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)
6
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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Events during cardiac cycle
• Atrial systole 0.1 second
• Atrial diastole 0.7 second
• Ventricular systole 0.3 second
 Isovolumic contraction 0.01 seconds
 Rapid ejection period
 Slow ejection period
• Ventricular diastole 0.5 seconds
 Isovolumic relaxation 0.02 seconds
 Rapid Passive filling phase
 Slow passive filling (Diastasis)
 Atrial contraction
Events during cardiac cycle
9
Events during cardiac cycle (continued)
Ventricular filling:
When ventricular pressure
falls below atrial pressure AV
valves opens & ventricular
filling begins
The first part of this period is
known as Rapid Passive
ventricular filling phase (3rd
heart sound)
Large part of ventricular filling
takes place during this period
Semilunar
valves closed
AV valves
opened
Events during cardiac cycle (continued)
Ventricular filling:
In the next phase of diastole
ventricular filling slows down .
As the ventricles are already
full to a large extent &
ventricular pressure slowly
rises
This phase is known as
diastasis or slow Passive
ventricular filling phase
Amount of filling during this
period is minimum
Semilunar
valves closed
AV valves
opened
Events during cardiac cycle (continued)
• Ventricular filling:
– Than comes the last
phase of ventricular
filling known as last
rapid filling
– This phase
corresponds with atrial
systole (contributes to
20-30% of ventricular
filling)
Semilunar
valves closed
AV valves
opened
Events during cardiac cycle
 Atrial systole:
 Caused by atrial
depolarization
 Left ventricle is relaxed
 As AV valves are open
,ventricles are filling with
blood even prior to atrial
systole
 Atrial systole causes further
increase in ventricular
volume
 Through out atrial
contraction atrial pressure
exceeds ventricular
pressure so AV valves
remain open
Semilunar
valves closed
AV valves
opened
Events during cardiac cycle (continued)
• Ventricular systole :
– After the atrial contraction impulse travels
through AV node & specialized conduction system
to excite the ventricle.
– As the ventricular contraction begins pressure in
the ventricles exceeds that of atria and this
backwards pressure forces the AV valves to close
Events during cardiac cycle (continued)
Isovolumetric ventricular
contraction:
To open the semilunar valves
ventricular pressure must
exceeds that of aortic &
pulmonary pressure
After closing of AV valves &
before opening of Semlunar
valves ,a brief period of time
when ventricles contracts as
a closed chamber
Ventricular pressure
continues to increase
Events during cardiac cycle (continued)
Semilunar
valves
opened
Semilunar
valves closed
AV valves
closed
AV valves
closed
Systole: Period
venticular ejection.
Events during cardiac cycle (continued)
• Ventricular diastole (repolarization):
– As the ventricles starts to relax on repolarisation
,ventricular pressure falls below aortic &
pulmonary pressure & semilunar valves closes .
Events during cardiac cycle (continued)
• Isovolumetric relaxation:
– when semilunar valves closes
AV valves is not yet open
because pressure in vetricles
still exceeeds that of atria.
– Therefore all valves are once
again closed for short period
of time when ventricles are
relaxing
Semilunar
valves closed
AV valves
closed
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. But still ventricular filling takes place is
adequate because maximum filling takes place
during first rapid PASSIVE filling phase
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21
Summary of events during cardiac
cycle
2. PRESSURE CHANGES DURING CARDIAC
CYCLE
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Events of cardiac cycle
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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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)
27
• 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.
SV (EDV – ESV)
EF =
X 100
EDV
75
X 100 = 62.5%
120
Normal ejection fraction is about 60 – 65 %.
Ejection fraction is good index of ventricular function.
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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;
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VD – Ventricular diastole
Relation ship of heart sounds with
events of cardiac cycle
1st heart sound = closure of AV valves at start of
ventricular systole
2nd heart sound= closure of semi lunar valves at
end of ventricular systole
3rd heart sound = first rapid filling phase
4th heart sound = end of ventricular filling phase
Heart Sounds
• We will discuss Heart Sounds in next lecture.
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References
• Text book of physiology by Linda .S .Costanzo
third edition
• Text book of physiology by Guyton & Hall
• review of medical physiology by william
F.Ganang