Cardiac beat
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Cardiac beat. Prof.Lammers CVS module/Week. The cardiac cycle. The cardiac cycle: the sequence of events from the beginning of one heart beat to the next one. It is made of: Systole: the phase of contraction and pumping blood Diastole: the phase of relaxation and filling .

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Cardiac beat

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Cardiac beat

Cardiac beat

Prof.Lammers

CVS module/Week


The cardiac cycle

The cardiac cycle

  • The cardiac cycle: the sequence of events from the beginning of one heart beat to the next one.

  • It is made of:

    • Systole: the phase of contraction and pumping blood

    • Diastole: the phase of relaxation and filling


The events during systole diastole

The events during Systole & Diastole

  • Diastole is made of three main phases:

    • Early diastole: rapid ventricular filling.

    • Middle diastole: ventricular filling in slower rate.

    • Late diastole: contraction of the atrium to pump extra 25% of blood to the ventricles.


The events during systole and diastole

The events during systole and Diastole

  • Systole is made of three phases:

    • Isovolemic contraction: after filling, AV valve closes & the semilunar valves is still closedpressure raise rapidly in the ventricles.

    • Ejection: when the pressure in the ventricles is higher than the pressure in the aorta/pulmonary artery semilunar valve openpumping blood out.

    • Isovolemic relaxation: after blood is pumped, pressure in the ventricles decreases & blood will try to flow back but the atrium pressure is higher than the ventricle AV valves openEARLY DIASTOLE


Pressure volume loop

Pressure-Volume loop

  • Phase I: ventricular filling  volume but pressure is 0

  • Phase II: isovolemic contraction  volume is constant but the pressure

  • Phase III: ejection  volume decreases and the pressure increases slightly and then decrease

  • Phase IV: isovolemic relaxation  volume is constant but the pressure decreases to 0.


Cardiac beat 1258795

Phase III

Phase IV

Phase II

Phase I


Regulation of the heart

Regulation of the heart

  • Intrinsic regulation of the heart is by Frank-Starling’s low: Blood volumeStretching of the heartforce of contraction.

    This is explained by the fact that when the muscle stretchthe actin & myosin filaments are brought to an optimal length degree of integration for force contraction.


Regulation of the heart1

Regulation of the heart

  • Extrinsic regulation of the heart: is by the sympathetic and parasympathetic system.

  • The sympathetic system: heart rate (+ chronotropic effect) & force of contraction ( + ionotropic effect)

  • The parasympathetic system (vagus nerve)  heart rate and had minimal effect on the force of contraction


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