The cardiac cycle describes the sequence of events in the heart from one heartbeat to the next. It involves rhythmic contractions and relaxations of the heart's chambers. Each cycle includes a systole, where the ventricles contract to pump blood out, and a diastole, where the ventricles relax and refill. The cycle is initiated by an electrical impulse from the sinoatrial node and involves pressure, volume, and valve changes in the heart chambers and arteries with each beat.

1. Cardiac Cycle

2. Cardiac Cycle
• Sequence of events from the beginning of one
systole to the beginning of next consecutive systole.
• One heart beat consists of one systole and one
diastole.
• Each cardiac cycle is initiated by the cardiac impulse
which originates from the SA node.
• During each cardiac cycle, certain events occur in
the heart and these include pressure changes,
volume changes, production of heart sounds,
closure and opening of heart valves and electrical
changes in the heart.

3. Cardiac Cycle
• Left ventricle
• Right ventricle
• Left atrium
• Right atrium
• Pulmunory Artery
• Aorta

4. Left Ventricle Cardiac Cycle Phases
• Isovolumetric Contraction Phase
• Maximal Ejection Phase
• Reduced Ejection Phase
• Protodiastole
• Isovolumetric Relaxation Phase
• Rapid Inflow/ Filling Phase
• Slow Filling Phase / Diastasis
• Atrial Systole

6. Isovolumetric Contraction Phase
• The left ventricle is full of blood just at the beginning of
ventricle systole. The pressure is 1-3 mm of Hg. And the
mitral valve is open.
• This phase starts with the closure of mitral valve.
• The ventricular muscle is contracting powerfully but
isometrically.
• Rapid increase in the ventricular pressure.
• No change in the blood volume i.e. remains at 120 ml
• When ventricular pressure reaches just above 80 mm
of Hg, there is opening of Aortic valve.
• So this phase starts with the closure of mitral valve and
ends with the opening of aortic valve.
• Duration is 0.06 seconds.

8. Maximal Ejection Phase
• With the opening of aortic valve, blood ejection
starts at maximal rate into aorta.
• Muscle is contracting powerfully but isotonically.
• Ventricular pressure rises to maximum 120 mm of
Hg.
• 2/3rd of Stroke volume(46 ml out of 70 ml) is
ejected in this phase.
• Duration is 0.11 seconds.

10. Reduced Ejection Phase
• The ventricular contraction becomes less powerful.
• Pressure falls from maximum.
• Remaining 1/3rd (24 ml out of 70 ml) of stroke
volume is ejected out.
• This phase ends when the ventricular pressure
becomes equal or slightly less than the aortic
pressure.
• Duration is 0.14 seconds.
• The above three phases constitute the ventricular
systole. This adds upto 0.31 seconds.

12. Protodiastole
• This is a short phase.
• Some blood flow continues from left ventricle into
aorta because of momentum, although ventricle
has stopped contracting.
• In this phase, the momentum has overcome by
further fall in ventricular pressure because of
relaxation.
• There is some backflow of blood in the first part of
aorta and aortic valve closes and with the closure of
this valve, the phase ends.
• Duration is 0.04 sec.

14. Isovolumetric Relaxation Phase
• Starts with closure of aortic valve.
• Ventricular muscle is undergoing relaxation
• Rapid fall in the ventricular pressure.
• No change in blood volume as both valves are
closed
• When the left ventricular pressure becomes lower
than the left atrial pressure, there is opening of
mitral valve. And then this phase ends.
• Duration is 0.06 sec

16. Rapid Inflow / Rapid Filling Phase
• Starts with the opening of mitral valve.
• Blood flows rapidly from left atrium into left
ventricle.
• Ventricle is undergoing relaxation so no rise in
pressure.
• There is 2/3rd filling of ventricle.
• Rapid filling phase remains for 0.11 sec.

18. Slow Filling Phase / Diastasis
• Stasis during the diastole
• In this phase, it appears that no blood is flowing from
left atrium into left ventricle.
• Most of the blood which was in left atrium has already
flown into left ventricle
• As mitral valve is open, small amount of blood returns
into left atrium from pulmonary veins and when this
blood enters into the atrium it directly goes into left
ventricle.
• So both left atrium and left ventricle acts as a single
chamber so it appears no blood is flowing into left
ventricle.
• Only slight filling occurs in this phase.
• Nearly no change in pressure or volume
• Duration is 0.20 sec

20. Atrial Systole
• Left atrium contracts to push the blood from its
cavity into left ventricle.
• With atrial systole, ventricular systole is completed.
• Atria contracts towards the end of the ventricular
diastole.
• Remaining 20-25% of the ventricular filling occurs.
• Duration is 0.11 sec
• The duration of whole ventricular diastole is 0.52
sec.

22. • Total cardiac cycle duration is 0.8 sec when heart rate is
about 72-75 beats /min.
• When heart rate increases, duration of cardiac cycle
decreases and this effects diastole more as compared
to systole. At a very rapid heart rate, diastole becomes
too short.
• At heart rate of 185 beats/min, the duration of cardiac
cycle is 0.33 sec and out of this 0.18 sec is systole and
diastole is 0.15 sec. so at a very rapid heart rate cardiac
output falls because of decreased duration of diastole
and so incompetent filling.
• The cardiac out put generally increases up to 150
beats/ min.
• No increase in cardiac output from 150-180.
• Beyond 180 beats/min cardiac output falls.

24. Right Ventricular Cardiac Cycle
• Same phases of the cardiac cycle with difference of
pressure values.
• At the start of the right ventricular systole, pressure
in the right ventricle is 0-1 mm of Hg.
• ISOMETRIC CONTRACTION PHASE:
• When pressure rises just above 8 mm of hg there is
opening of the pulmonary valve.
• MAXIMAL EJECTION PHASE:
• Pressure rises maximally to 25 mm of Hg.

26. ATRIAL PRESSURE CHANGES
• Atria also undergoes systole and diastole.
• Duration of atrial systole is 0.11 sec where as atrial
diastole is 0.7 sec. so much prolonged atrial diastole
which helps in filling.
• During each cardiac cycle, three waves are recorded
from atria i.e. a wave, c wave and v wave.
• A wave
• C wave
• V wave

27. ATRIAL PRESSURE CHANGES
• A wave:
• Due to rise in the atrial pressure during systole.
• C wave:
• Occurs at the beginning of ventricular systole. During
isometric contraction, there is rapid rise in ventricular
pressure, there is bulging of the AV valve into atria and thus
increasing atrial pressure and this gives the ascend of c wave.
The top of the c wave coincides with the opening of
semilunar valves, ventricular contracts more powerfully ,
contraction of myocardial fibers so av valve is pulled back to
ventricales and this causes decreased pressure in atria leading
to descent of c wave.
• V wave : due to gradual rise in atrial pressure, when blood
accumulates in the atria because of closed av valves. The top
of v wave coincides with the opening if av valves. The blood
flows from atrium to ventricles rapidly causing descent of v
wave.

29. ATRIAL PRESSURE CHANGES
• In the right atrium, the pressure may rise upto 4 -5
mm of hg. And in left atrium the pressure may rise
upto 6-8 m of hg.
• Pulsations recorded from jugular vein is called JVP.
JVP is due to backward transmission of pressure
changes of right atrium to neck veins and so in JVP
we see same waves.

30. PRESSURE CHANGES IN AORTA
• Maximum pressure is during left ventricular systole.
i.e. 120 mm of hg.
• Minimum pressure is during left ventricular diastole
i.e. 80 mm of hg.
• In aortic pressure curve there is incisura. A sharp
rise in the aortic pressure followed by a gradual fall.
• Inciusra is recorded at the time of closure of aortic
valve.

32. PRESSURE CHANGES IN PULMUNORY
ARTERY
• Maximum pressure is 25 mm of hg during right
vebtricular systole.
• Minimum pressure is 8 mm of hg during right
ventriculkar diastole.

33. • SEQUENCE OF SYSTOLE IN THE FOUR CHAMBERS OF
HEART:
• Right atrial systole precedes left atrial systole.
• Left ventricular systole begins slightly earlier than
the right ventricuylar systole, but blood ejection
into the pulmunory artery begins earlier because of
low pressure in pulmunory artery than in aorta.