1.
PRESENTATION
TOPIC : EVENTS IN
CARDIAC CYCLE
PRESENTED BY : AKSHITA MENGI
ROLLNO. : 12
CLASS : MSC ZOOLOGY SEM 3RD
MINOR 2 PRESENTATION

2.
CARDIAC CYCLE
Cardiac cycle is defined as the succession
of coordinated events taking place in the
heart during each beat.
Each heartbeat consists of two major
periods called systole and diastole .
During systole heart contracts and pumps
the blood through arteries during diastole
the heart relaxes, blood is filled in the
heart.

3.
EVENTS OF CARDIAC CYCLE
Atrial events
ventricular events
Duration :when the heart beats at a normal rate of 72
/minutes duration of each cardiac cycle is about 0.8
second .
Atrial events : Atrial systole= (0.1) sec
Atrial diastole =(0.7) sec
Ventricular events : Ventricular systole = 0.3 sec

4.
In each cardiac cycle the atria and the ventricals
are directly contract and relax forcing blood from
areas of high pressure to area of lower pressure .
As a Chamber of heart contracts blood pressure
within it increases.
Cardiac cycle is initiated by actions potential in SA
node.

5.
STAGES
ATRIAL SYSTOLE : During atrial systole which last for 0.1 second the atria
are contracting at the same time ventricles are relaxed.
The depolarisation of SA node causes atrial depolarization. Atrial
depolarization causes atrial systole.
As atria contract, they exert pressure on blood which forces blood
through the open auricular ventricular valve into ventricle .
Atrial systole contributes a final 25 ml of blood to the volume already
present in the ventricles about( 105 ml ).
End of atrial systole is also the end of ventricular diastole .Thus each
ventricle contains about 130 ml at and of its relaxation period .This
volume is known as end diastolic volume (EDV).

6.
VENTRICULAR SYSTOLE
It last for 0.3 seconds ,the ventricles are contracting. At the same time, the
atria are relaxed in atrial diastole.
Ventricular depolarization causes ventricular systole. As ventricular systole
begins ,pressure rises inside ventricles and pushes blood up against the
atrio-ventricular valve forcing them shut.
Closure of AV valves results in first heart sound. Both the semi lunar and
AV valves are closed for 0.05 seconds.
This is the period of iso volumetric contraction .
During the period cardiac muscle fibres are contracting and exciting force
but are not shortening and ventricular volume remains same (isovolumic)

7.
RAPID EJECTION
Continued contraction causes pressure inside the chamber to
rise sharply When left ventricular pressure surpasses aortic
pressure at about 80 mmhg and right ventricular pressure
rises in the pulmonary trunk about 20 mmhg both the SL
valves open.
At this point ejection of blood from right ventricle to
Pulmonary artery and from left ventricle to aorta occurs. This
period last for 0.25 seconds.
The pressure in the left ventricle continuous to rise about
120 mmhg.
Reduced ejection : Then because repolarization in ventricles
starts contraction becomes slow and ejection from heart
becomes slow.The left ventricle ejects about 70 ml of blood

8.
STROKE VOLUME
THEVOLUME EJECTED PER BEAT FROM EACH
VENTRICLE IS END DIASTOLIC VOLUME – END
SYSTOLIC VOLUME.
SV = EDV – ESV
AT REST SV IS ABOUT 130ML – 60 ML = 70ML

9.
RELAXATION PERIOD
During relaxation period which last for 0.4 seconds the
atria and ventricles are both relaxed .
Ventricular repolarization causes ventricular diastole. As
ventricle relax pressure within chambers falls and blood
in aorta and pulmonary trunk begin to flow backward
towards the region of lower pressure in ventricles.
Back flowing of blood catches in the valve cusps and
closes the SL valves and thats when the second heart
sound is heard. After the SL valve close ,there is brief
period when ventricular volume does not change
because all the four valves are closed. This is the period

10.
RAPID FILLING
As the ventricles continues to relax the pressure falls quickly
.When ventricular pressure drops below the atrial pressure the,
AV valves open and ventricular filling begins.
The major part of ventricular filling occurs just after AV valve
open. Blood that has been flowing into and building up in atria
during isovolumetric ventricular relaxation rashes rapidly into
ventricles.
At the end of relaxation period the ventricles are about three
quarters full. So 90% of ventricular filling occurs before atrial
contraction and is passive.

11.
REDUCED FILLING
Slowly pressure starts building up in ventricles
again and reduces the atrial- ventricular pressure
so filling becomes slow i.e and rest of the blood
is filled after atrium contraction.

12.
HEART SOUNDS
TWO HEART SOUNDS SEPARATED BY SHORT PAUSE CAN
EASILY BE DISTINGUISHED. THEY ARE DESCRIBED IN WORDS
AS “LUBDUP”.
THE FIRST SOUND LUB IS LOUD AND DUE TO CLOSURE OF
ATRIOVENTRICULAR VALVE . THIS CORRESPONDS WITH
VENTRICULAR SYSTOLE.
THE SECOND SOUND IS DUP IS SOFTER AND DUE TO
CLOSURE OF AORTIC AND PULMONARY VALVES. THIS
CORRESPONDS WITH ATRIAL SYSTOLE .

13.
Left ventricle > Right ventricle > Left
auricle> Right auricle
120 mmHg. 25/30 mmhg.
7/8mmhg. 4/8 mmhg
PRESSURE
DIFFERENCE

14.
THANK YOU