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Phases of the Cardiac CyclePhases of the Cardiac Cycle!  All the events associated with the flow of blood through the heart during

a single complete heartbeat (approx 0.8sec if heart rate is 75bpm)

!! OneOne ““heart beatheart beat”” may be divided into two sequential phases:may be divided into two sequential phases:

!! DiastoleDiastole

!! Period of cardiac relaxationPeriod of cardiac relaxation

""

Often an implied time of refilling, despite period of isovolumetricOften an implied time of refilling, despite period of isovolumetricrelaxationrelaxation

!! SystoleSystole

!! Period of cardiac contractionPeriod of cardiac contraction

"" Often an implied time of ejection, despite period of isovolumetricOften an implied time of ejection, despite period of isovolumetriccontractioncontraction

!! Each phase may be applied to both atria and ventricles, therefore theEach phase may be applied to both atria and ventricles, therefore thesequence of events (which may overlap) are:sequence of events (which may overlap) are:

!! atrial diastoleatrial diastole !! ventricular diastoleventricular diastole !! atrial systoleatrial systole !! ventricular ventricular systolesystole

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Phases of the Cardiac CyclePhases of the Cardiac Cycle! Revise:

! Cardiac anatomy

!  Action of valves

! Valves open passively due to pressure gradients

!  AV valves open when P atria > P ventricles

! Semilunar valves open when P ventricles > P arteries

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Cardiac Cycle:Cardiac Cycle:

Mechanical PhasesMechanical Phases

START

5

4

1

2

3

Late diastole: both sets of chambers are relaxed andventricles fill passively.

Atrial systole: atrial contractionforces a small amount ofadditional blood into ventricles.

Isovolumic ventricularcontraction: first phase ofventricular contraction pushesAV valves closed but does notcreate enough pressure to opensemilunar valves.

Isovolumic ventricular relaxation: as ventriclesrelax, pressure in ventriclesfalls, blood flows back intocups of semilunar valvesand snaps them closed.

Ventricular ejection:as ventricular pressurerises and exceeds

pressure in the arteries,the semilunar valvesopen and blood isejected.

SilverthornSilverthorn, fig 14-24, step 1-5, fig 14-24, step 1-5

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Ventricular Volume and StrokeVentricular Volume and Stroke

VolumeVolume

EDV = end diastolic volume = volume of blood in ventricle at end of diastole

ESV = end systolic volume = volume of blood in ventricle at end of systole

SV = stroke volume = volume of blood ejected from heart each cycle

SV = EDV - ESV

130 mL – 70 mL = 60 mL

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Cardiac Cycle:Cardiac Cycle:

Pressure-Volume curve/loopPressure-Volume curve/loop

AB

C

0 65 100 135

Left ventricular volume (mL)

120

80

40EDV

ESV

D

Stroke volume

KEY

EDV = End-diastolic volume

ESV = End-systolic volume

One

cardiac

cycle

   L  e   f   t  v  e  n   t  r   i  c  u   l  a  r  p  r  e  s  s  u  r  e   (  m

  m    H

  g   )

SilverthornSilverthorn, fig 14-25, (4 of 4), fig 14-25, (4 of 4)

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WiggersWiggers’’ DiagramDiagram

Electro-cardiogram

(ECG) P

Cardiac cycle

Atrialsystole

Atrialsystole

Ventricular systole

Ventricular diastole

PT

Atrial systole Ventricular  systole

Atrialsystole

Time (msec)

0 100 200 300 400 500 600 700 800

Earlyventricular 

diastole

Lateventricular 

diastole

Isovolumicventricularcontraction

QRScomplex

QRScomplex

SilverthornSilverthorn, fig 14-26, (1 of 13), fig 14-26, (1 of 13)

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WiggersWiggers’’ DiagramDiagram

Electro-cardiogram

(ECG)

Pressure(mm Hg)

Heartsounds

Leftventricular 

volume(mL)

Dicroticnotch

P

Cardiac cycle

Atrialsystole

Atrialsystole

Ventricular systole

Ventricular diastole

PT

S2S1

Atrial systole Ventricular  systole

Atrialsystole

Leftventricular pressure

Left atrialpressure

65

135

30

60

90

120

Time (msec)

0 100 200 300 400 500 600 700 800

Ao r t a 

Earlyventricular 

diastole

Lateventricular 

diastole

Isovolumicventricularcontraction

QRScomplex

QRScomplex

SilverthornSilverthorn, fig 14-26, (13 of 13), fig 14-26, (13 of 13)

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Boron &Boron & BoulpaepBoulpaep, fig 21-1, fig 21-1