1. Structure and Function
The Mammalian Heart
Structure and Function
© SSER Ltd.
P A JOY

2. Lesson Aims To examine the cardiac cycle
To p12 “the pressure gets less and less…”

3. The Cardiac Cycle At the end of atrial When muscles contract without
systole, the volume of
blood in the ventricles
is such that the AV
valves are forced closed
When muscles contract without
changing in length, this is known
as isometric contraction
Muscle contraction involving the
shortening of muscle fibres is
known as isotonic contraction
There is now a situation
where the AV and the
semilunar valves are
both closed, the atria
are relaxed and the
ventricles enter a
phase of contraction
or SYSTOLE
The ventricles are
undergoing isometric
contraction with the
volume of blood in the
ventricles remaining
constant and the pressure
building up
The ventricles are now
contracting but the sheer
load of blood on the
ventricle muscles prevents
them from shortening
When the rising pressure
exceeds that in the aorta
and pulmonary arteries,
the semilunar valves are
forced open and blood is
ejected from the heart as the
ventricle muscles shorten
Ventricular systole is taking
place but the muscle cells are
unable to change in length
This phase of the heartbeat
is known as
VENTRICULAR
EJECTION
This phase of the heartbeat is known as
ISOMETRIC VENTRICULAR CONTRACTION

4. Ventricular Systole involves two phases
The Cardiac Cycle
To summarise:
Ventricular Systole involves two phases
Isometric ventricular contraction when;
the ventricle muscles contract without
changing in length
the volume of blood in the ventricles
remains constant
pressure builds up in the ventricles
Ventricular ejection when;
the semilunar valves are forced open
the ventricle muscles contract in an
isotonic fashion (they shorten)
blood is ejected into the aorta and
pulmonary arteries
At the end of ventricular systole, the ventricles begin to relax and the
pressures drop below those in the aorta and pulmonary arteries
A brief backflow of blood in the arteries closes the semilunar valves

5. The Cardiac Cycle
As the ventricles relax, closure of the semilunar valves occurs due to a
brief backflow of blood from the aorta and pulmonary arteries
This phase of the heartbeat
is known as
VENTRICULAR
RELAXATION
(Early Diastole)
The pressures in the
ventricles continue to fall
and reach very low
values
When the pressures
in the ventricles fall
below those of the
atria, the AV valves
open

6. The Cardiac Cycle
As the ventricles relax, closure of the semilunar valves occurs due to a
brief backflow of blood from the aorta and pulmonary arteries
This phase of the heartbeat
is known as
VENTRICULAR
RELAXATION
(Early Diastole)
The pressures in the
ventricles continue to fall
and reach very low
values
When the pressures
in the ventricles fall
below those of the
atria, the AV valves
open
Passive filling of the ventricles (late diastole) occurs
as the cycle begins again

7. close as the ventricles
Late Diastole &
Atrial Systole
Ventricular Systole
(Isometric Phase)
AV valves open,
semi-lunar valves
closed
AV valves close
at the end of
atrial systole
All valves closed
as the ventricle
muscles contract
without shortening
(Isometric
Contraction)
Passive filling
of the ventricles
followed by
atrial systole
SUMMARY
Pressure builds
up in the
ventricles
Ventricular
Relaxation
Ventricular Systole
(Ejection)
Semi-lunar valves
close as the ventricles
begin to relax
Semi-lunar valves
open and blood
is ejected into
the aorta and
pulmonary artery
Pressure in the
ventricles falls
to a very low
value and the
AV valves open
Muscles shorten
as they contract

8. Pressure Changes during The Cardiac Cycle
Throughout the cardiac cycle, pressure changes take place
in the atria, ventricles and arteries
Pressures in the right and left atrium, right and left ventricle, aorta
and pulmonary arteries can be recorded and illustrated in
graphical form
The graph on the next slide shows pressure changes in the left side of
the heart and the aorta
A similar graph can be drawn for the right side of the heart and the
pulmonary arteries
Such a graph is similar in shape to that obtained for the left side
of the heart but all the pressures readings are of a lower value

9. Pressure Changes in the
Left Side of the Heart
During One Cardiac
Cycle
left ventricular
pressure
aortic
pressure
The pressure changes
in the left ventricle,
left atrium and aorta
can be related to the
phases of the cardiac
cycle
left atrial
pressure

10. aortic pressure left ventricular left atrial
Pressure Changes in the
Left Side of the Heart W A X Y A Z
Period Z to A represents
the phase of Passive Filling
of the ventricles when the
AV valves are open and
the semi-lunar valves are closed
aortic
pressure
left ventricular
left atrial
Period A to W represents
the phase of Atrial Systole
when the atria contract
and the ventricles are
filled to full capacity
Period W to X represents
the first phase of
Ventricular Systole when
the ventricles contract in an
isometric fashion; the
greatest rise in ventricular
pressure occurs during this
phase and the ventricular
volume remains constant
Period X to Y represents the
second phase of Ventricular
Systole when ejection of blood
takes place and pressure in the
aorta rises
Period Y to Z represents relaxation
of the ventricles (diastole) when the
ventricular pressure drops sharply

11. The facts you need to know
From p11 “systole is the term used…”
To p12 “the pressure gets less and less…”