The cardiac cycle consists of 4 phases: 1) Isovolumetric contraction - the ventricles contract but volume remains constant until the aortic valve opens 2) Ventricular ejection - the aortic valve opens and blood is ejected from the ventricles into the aorta 3) Isovolumetric relaxation - the ventricles relax but volume is constant until the mitral valve opens 4) Ventricular filling - the mitral valve opens and the ventricles fill with blood from the atria in preparation for the next cycle.

1. The Cardiac Cycle
Charlotte Richardson

2. The cardiac cycle
This presentation goes through the stages of the
cardiac cycle that occur in one full contraction
of the heart.

3. The cardiac cycle
There are four stages of the cardiac cycle:
I. Isovolumetric contraction
II. Ventricular ejection
III. Isovolumetric relaxation
IV. Ventricular filling

4. The cardiac cycle
Broadly the stages of the cardiac cycle can be
divided into systole and diastole:
I. Isovolumetric contraction
Systole- when the ventricles
II. Ventricular ejection are contracting
III. Isovolumetric relaxation
Diastole- when the
IV. Ventricular filling ventricles are relaxing
Here the cycle has been depicted as starting from the end of
diastole when the ventricles are relaxed and filled with blood

5. Phase 1: Isovolumetric Contraction
The left ventricle is
full of blood and
begins to contract.
This causes the
pressure in the left Aortic pressure
ventricle to increase.
PRESSURE (mmHg)
Left atrial pressure
Left ventricular
pressure
Left ventricular
IV I II III IV
pressure
PHASE OF THE CARDIAC CYCLE

6. Phase 1: Isovolumetric Contraction
Once the pressure in
the left ventricle
exceeds that of the
left atrium the mitral
valve will close.
Aortic pressure
This is to prevent
PRESSURE (mmHg)
blood from going
back into the left
atrium.
Mitral valve closes
Left atrial pressure
Left ventricular
pressure
Left ventricular
IV I II III IV
pressure
PHASE OF THE CARDIAC CYCLE

7. Phase 1: Isovolumetric Contraction
The ventricles
continue to
contract, but until the
aortic valve opens the
pressure in the left
ventricle increases Aortic pressure
with no change in
PRESSURE (mmHg)
volume- this is
isovolumetric
contraction. Isovolumetric
contraction
Left atrial pressure
Left ventricular
pressure
Left ventricular
IV I II III IV
pressure
PHASE OF THE CARDIAC CYCLE

8. Phase 2: Ventricular ejection
Once the pressure in
the left ventricle
exceeds that of the
aorta the aortic valve
will open.
PRESSURE (mmHg) Aortic pressure
Aortic valve opens
Left atrial pressure
Left ventricular
pressure
Left ventricular
IV I II III IV
pressure
PHASE OF THE CARDIAC CYCLE

9. Phase 2: Ventricular ejection
Blood then leaves
the left ventricle into Ventricular ejection
the systemic
circulation via the
aorta- ventricular
ejection Aortic pressure
PRESSURE (mmHg)
Left atrial pressure
Left ventricular
pressure
Left ventricular
IV I II III IV
pressure
PHASE OF THE CARDIAC CYCLE

10. Phase 3: Isovolumetric relaxation
The ventricles now
begin to relax once
Aortic valve closes
the blood has been
ejected.
When the pressure Aortic pressure
in the left ventricle
PRESSURE (mmHg)
falls below that of
the aorta the aortic
valve will close. This
prevents blood
flowing back into the
left ventricle from Left atrial pressure
the aorta. Left ventricular
pressure
Left ventricular
IV I II III IV
pressure
PHASE OF THE CARDIAC CYCLE

11. Phase 3: Isovolumetric relaxation
As the ventricles
relax the pressure
will fall, but there
will be no change in
volume until the
mitral valve opens- Aortic pressure
this is isovolumetric
PRESSURE (mmHg)
relaxation Isovolumeteric
relaxation
Left atrial pressure
Left ventricular
pressure
Left ventricular
IV I II III IV
pressure
PHASE OF THE CARDIAC CYCLE

12. Phase 4: Ventricular filling
Once the pressure in
the left ventricle falls
below that in the left
atrium the mitral
valve will open.
Aortic pressure
This then allows the
PRESSURE (mmHg)
ventricles to fill with
blood from the left
atrium, preparing
the ventricles for Mitral valve opens
another round of the
cardiac cycle. Left atrial pressure
Left ventricular
pressure
Left ventricular
IV I II III IV
pressure
PHASE OF THE CARDIAC CYCLE

13. The cardiac cycle- recap
Phases of the cardiac cycle:
I. Isovolumetric contraction
Systole
II. Ventricular ejection
III. Isovolumetric relaxation
Diastole
IV. Ventricular filling

14. The cardiac cycle- recap
Ventricular ejection
Aortic valve closes
PRESSURE (mmHg)
Aortic pressure
Aortic valve opens
Isovolumeteric
Isovolumetric relaxation
contraction
Mitral valve opens
Mitral valve closes
Left atrial pressure
Left ventricular
pressure
IV I II III IV
PHASE OF THE CARDIAC CYCLE