This document summarizes the cardiac cycle and its seven phases: 1) atrial systole, 2) isovolumetric ventricular contraction, 3) rapid ventricular ejection, 4) reduced ventricular ejection, 5) isovolumetric ventricular relaxation, 6) rapid ventricular filling, and 7) reduced ventricular filling. It describes the relationship between pressures, volumes, and heart sounds in the left atrium and ventricle, aorta, and jugular vein throughout each phase of the cycle. It also discusses how arrhythmias like tachycardia and atrial fibrillation can impact the cardiac cycle by reducing stroke volume and cardiac output.

1. CVS Physiology III
Cardiac Cycle
Faiz Baherin MBBS
Mmed (Emergency) Training Programme USM
Supervisor : A.Prof Nasir

2. Outline
• Introduction
• Relationship between pressure, volume,
heart sounds in the left atrium and
ventricle, aorta and jugular vein in one
cardiac cycle
• Applied physiology – changes during
arrhythmia

3. Cardiac Cycle
• One complete sequence of ventricular
systole and diastole
• Cycle of events that occurs as the heart
contracts and relaxes
• Both sides of heart
• Takes approximately 0.8 secs at a heart
rate of 72 beats per minute

4. Cardiac Cycle
• Divided into seven phases (and duration of
phases)
1)Atrial Systole (0.11s – 0.53s)
2)Isovolumetric Ventricular Contraction (0.05s)
3)Rapid Ventricular Ejection (0.22-0.27s)
4)Reduced Ventricular Ejection (0.22-0.27s)
5)Isovolumetric Ventricular Relaxation (0.08s )
6) Rapid Ventricular Filling (0.11s)
7) Reduced Ventricular Filling (0.19s)

5. Cardiac Cycle

6. 1) Atrial Systole
- Mitral valve is already
open and blood passively
flows into the ventricle
(from previous cycle)
approx 80 %
- During this phase,
contraction of the atrium
tops up the ventricular
volume – remaining 20%
EDV - 120ml
- Ventricle relaxes

7. 1) Atrial Systole
-The "a" wave occurs
when the atrium
contracts, increasing
atrial pressure.
-Blood arriving at the
heart flows back up the
jugular vein, causing the
first wave in the jugular
venous pulse.
-Ventricle pressure is not
raised

8. 1) Atrial Systole – ECG & Heart sounds
-Preceded by p wave on ECG
-marks the depolarization of atria
-S4, heard in ventricular hypertrophy
-Atria contracts against a stiffened
ventricle

9. 2) Isovolumetric Ventricular
Contraction
-Left ventricles begins to
contract
-Increase in LVP
-Mitral valve closes
-Ventricular volume
remains the same
(approximately 120ml)

10. 2) Isovolumetric Contraction
- LV pressure builds
up
- LV volume remains
constant (both
valves are close)
- C wave – bulging
of mitral valve
back to atrium –
slight increase in
pressure

11. 2) Isovolumetric Contraction – ECG
and heart sounds
-QRS Complex
-Represents the ventricular depolarization
-1st heart sound – S1
-Closure of the mitral valve

12. 3) Rapid Ventricular Ejection
-Ventricular continues
contracting
-Pressure increased,
greater than the aortic
pressure (80mmhg)
-Opening of aortic valve
-Most of stroke volume
(almost 70ml) ejected
during this phase,
-reduce LV volume

13. 3) Rapid Ventricular Ejection
- Increase in LVP
- Increase in Aortic
pressure due to
volume of blood
ejected
- Reduce in LV
Volume

14. 4) Reduced ventricular Ejection
-Ventricular pressure
falls
-Aortic pressure falls
-Remaining of LV
volume still being
ejected, due to kinetic
energy, with reduced
rate

15. 4) Reduced ventricular Ejection
-Reduced both aortic and
ventricular pressure
-Reduced LV volume
-Slight increase in LA
pressure
-T wave
-ventricles starts
repolarizing

16. 5) Isovolumetric Ventricular Relaxation
-Left ventricle relaxes
-Reduce pressure in
LV
-Aortic valve closes
-LV volume constant –
End systolic Volume
(approximately 50ml)
SV = EDV – ESV =
70ml

17. 5) Isovolumetric Ventricular Relaxation
- Reduced LV
Pressure
- Incisura in aorta
- LV Volume
constant
- LA pressure
increases

18. 5) Isovolumetric Ventricular Relaxation
– Heart Sound
- S2 due to aortic valve closure
- Splitting of heart sounds – during inspiration –
decrease in intrathoracic pressure – increase
in venous return to right side of hard, increase
in stroke volume, prolongs ejection time,
delays closure of pulmonary valve

19. 6) Rapid Ventricular Filling
-LV relaxes
-LV pressure falls to its
lowest level and
constant
-Mitral valve opens
-LV volume increases
rapidly

20. 6) Rapid Ventricular Filling
- LV pressure reduces
and remains the
same(high
compliance)
- Aortic pressure
decreases
- LA pressure
decreases
- LV volume increases

21. 6) Rapid Ventricular Filling – heart
sound
- S3 – normal in children but not adult
- Indicates volume overload as in CCF,
mitral regurge
- Occurs due to passive, rapid ventricular
filling
- No ECG deflection

22. 7) Reduced Ventricular Filling
- Diastasis
- Longest phase in
cardiac cyle
- Final portion of
ventricular filling,
slower rate
- LV volume increases
- Increase in heart rate
alters this phase

23. Arrhythmia
• Tachycardia of atrial or ventricular origin
reduces stroke volume and cardiac output
particularly when the ventricular rate is
greater than 160 beats/min.
• The stroke volume becomes reduced because
of decreased ventricular filling time and
decreased ventricular filling at high rates of
contraction

24. Arrhythmia
• If the tachyarrhythmia is associated with
abnormal ventricular conduction, the synchrony
and effectiveness of ventricular contraction will
be impaired leading to reduced ejection
Hence 1) reduced filling time
2) reduced filling
3) reduced ejection
And all will contribute to less cardiac output

25. Arrhythmia – Atrial Fibrillation
• Concept of atrial kick – contribution of atrial
systole in ventricular filling – added 10-20% of
ventricular volume, during exercise, up to 40%
• Therefore, atrial fibrillation generally has
relatively minor hemodynamic consequence
at rest, but can significantly limit normal
increases in ventricular stroke volume and
cardiac output during exercise.

26. Arrhythmia – Atrial Fibrillation
• In hypertrophy – reduce compliance -
increased ventricular stiffness impairs passive
filling, atrial contraction contributes
significantly to ventricular filling even at rest.
• In AF, loss of atrial kick, reduced filling time,
reduced filling, ineffective ejection - CO is
significantly affected – hemodynamic
instability

27. Thank you

28. Reference
• Physiology, Linda S. Costanzo 4th Edition