Trouble in understanding graph of pressure time in different chambers of heart ![heart]( In the book, it is written that from _0 s to 0.125 s_ - **Atrial Systole** ; _0.125 s to 0.325 s_ - **Ventricular Systole** ;

Trouble in understanding graph of pressure time in different chambers of heart ![heart]( In the book, it is written that from _0 s to 0.125 s_ - Atrial Systole ; _0.125 s to 0.325 s_ - Ventricular Systole ; _0.325 s to 0.6 s_ - Ventricular Diastole Why a bump is there from 0.125 s to about 0.175 s in the pressure-time graph of left atrial pressure and why is the pressure in the left auricle increasing during the ventricular systole and ventricular diastole stage (from 0.175 s to 0.45 s)?

A previous Biology.SE question has a diagram with a bit more information on it...

![enter image description here](

When the ventricles starts to contract, the AV valves close as the pressure rises very quickly in the ventricle and exceeds that of the atria; the blood in the atrium is going to be squeezed a bit at that point between the atrial wall and AV valve, that's the little uptick "0.125 s to 0.325 s".

From 0.175 s to 0.45 s the AV valves are still closed but blood is trickling into the atria and they're getting passively distended. You can see the pressure drops again when the AV valves open and the ventricles begin to fill from the atria.