Cardio 10 – Mechanical Properties of the Heart II
Anil Chopra
Event
1. Describe the events of the cardiac cycle.
Mechanics
ECG
Atrial Systole
aortic, ventricle, atrial
Isovolumetric Contraction
aortic, ventricle, atrial
Rapid Ejection
aortic, ventricle, atrial
Sound
Atria contract to top off
blood in the ventricles
(some has already flown
through the AV valve.
Some blood is pushed
back up the jugular vein.
Produces P-wave as SAN
depolarises atria.
None, but can produce 4th
heart sound in congestive
heart failure, pulmonary
embolism & tricuspid
incompetence.
The small interval where
the atrio- ventricular
valves are closed and the
semi lunar valves are
closed. There is high
pressure in the ventricles
QRS complex as ventricles
depolarise.
First “lub” as AV valves
close.
Ventricles contract
causing the high pressure
to force open the semilunar valves.
No depolarisation.
None.
Reduced Ejection
aortic, ventricle, atrial
Isovolumetric Relaxation
aortic, ventricle, atrial
Rapid Ventricular Filling
aortic, ventricle, atrial
Reduced Ventricular Filling
aortic, ventricle, atrial
Marks the end of systole.
Ventricular volume
decreases. SL valves
begin to close.
T-wave due to ventricular
depolarisation
None.
The beginning of
diastole. Aortic and
pulmonary valves are
shut as blood falls back
through the aorta.
None.
2nd heart sound “dub” as
semilunar valves close.
The AV valves are open
and so blood rapidly
flows from veins, to atria
to ventricles. This
increases ventricular
volume
None
Can produce 3rd heart sound
in hypertension or mitral
incompetence.
Simply, the ventricles fill
more slowly as
atrioventricular valves
are open
None
None.
2. Use a graph to correlate electrocardiographic events and pressure events of the
atria, ventricles aorta and pulmonary artery.
3. Indicate on the graph, the phases of the cardiac cycle and the corresponding
pressure changes, valve openings and closures.
Pressure change
patterns are the
same for left and
right ventricles.
Aortic Valve Opens
Aortic Valve Shuts
Quantitatively,
right pressures
are lower.
Mirtal Valve Shuts
Mitral Valve Opens
Amount of blood
ejected from each
ventricle is the
same
4. Define and
State normal
values for
right and left
ventricular
end-diastolic
volume, end
systolic
volume, stroke volume, end diastolic pressure and peak systolic pressure.
End Diastolic Volume: volume of blood in the ventricles after filling.
 Usually around 130ml.
End systolic Volume: volume of blood in the ventricles after systole.
 Usually around 60ml.

Stroke Volume: volume of blood ejected by ventricular contraction.
 Usually around 70ml.
End Diastolic Volume = stroke volume + end systolic volume
Left End Systolic Pressure: pressure of left ventricle systole.
 Usually around 120mmHg.
Left End Diastolic Pressure: pressure of left ventricle diastole.
 Usually around 80mmHg.
Mean left Atrial Pressure:
 Usually between 8-10mmHg.
Right End Systolic Pressure: pressure of right ventricle systole.
 Usually around 25mmHg.
Right End Diastolic Pressure: pressure of right ventricle diastole.
 Usually around 5mmHg.
Mean right Atrial Pressure:
 Usually between 0-8mmHg.
5. State the origin of the heart sounds.
Lub – Atrioventricular valves closing
Dub – semilunar valves closing.
6. Provide the mathematical equation for ejection fraction. Define cardiac output and
indicate its determinants.
Ejection Fraction: % of end diastolic volume ejected.
 Usually around 54%
 Can be up to 80% in exercise or 40% during heart failure.
Cardiac Output: amount of blood pumped out each ventricle per minute; calculated
by heart rate x stroke volume.
 Usually around 5litres.
7. Construct Simple volume-pressure diagrams from the events during the cardiac
cycle and annotate the graphs appropriately.
1) Ventricles full (end diastolic volume)
Preload.
2) Ventricles contract and meet aortic pressure.
Afterload encountered.
3) Ventricles empty (end diastolic volume) but ventricles still
contracted.
4) Ventricles are relaxed and empty so pressure is low, as is volume.
INCREASING PRELOAD INCREASES STROKE VOLUME
(Frank – Starling relationships)
These increases can be as a result of sympathetic stimulation of the heart during
exercise. If the ventricles fill with more blood in diastole, the heart contracts with
more force so greater stroke volume is achieved.