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Background:It is said that during the phase of isovolumetric contraction , due to sharp rise in the ventricular pressure, there occurs bulging of AV valves into the atria producing a small but sharp rise in the intra-atrial pressure called c-wave.( in the second cycle of diagram).

Cardiac cycle,guyton and hall


Question: I am unable to understand why is then pressure in atria falling after the end of isovolumetric phase, even though the pressure in the ventricles is rising, so this should further bulge the AV valve or atleast( due to action of papillary muscles) have same pressure, So why is pressure falling?

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The curve you are talking about is JVPJuglar Venous Pressure Curve.enter image description here

You are talking avoit x-decent after c pulse. The downward deflections of x decent is produced by the atrium relaxation and the downward movement tricuspid valve.

This causes decrease in atrial pressure.

A new fascinating question could be why x-decent is greater than y-decent. Good luck.

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