Postgraduate Medicine: Congestive Heart Failure Symposium: Diastolic Heart Failure

Postgraduate Medicine: Congestive Heart Failure Symposium: Diastolic Heart Failure:
It is work to relax???

This image shows Aortic pressure as well as pressure in the left ventricle and left atrium. The phases listed are those of diastole (systole is on the left near zero and not discussed in this text). One remarkable thing about this graph is it says the atrium never sees high pressure... It is just a low pressure volume pump? Anyway, Here is the picture:
"What is normal diastole?
Diastole consists of four hemodynamic phases. The first phase, isovolumic relaxation, extends from aortic valve closure to mitral valve opening, during which the left ventricular volume remains constant as left ventricular pressure falls with myocardial relaxation. Although overall left ventricular volume does not change during this phase, changes in left ventricular shape may occur.
The second phase of diastole is the rapid filling phase, which begins when left ventricular pressure falls below left atrial pressure, opening the mitral valve. During this phase, left ventricular pressure falls despite increasing left ventricular volume. This creates a vacuum that assists in diastolic filling. Rapid filling continues until the pressures in the atrial and ventricular chambers equalize and ventricular filling stops, marking the beginning of the third phase, termed diastasis.
During diastasis, left atrial and left ventricular pressures are in equilibrium and little filling occurs. The final phase of diastole is atrial contraction, which contributes about 15% to 25% of the total left ventricular filling in normal subjects.
Left ventricular diastolic relaxation proceeds as calcium is released from its binding site on troponin-C, allowing the actin-myosin cross-bridges to dissociate. This free cytoplasmic calcium must then be taken up into the sarcoplasmic reticulum against a large concentration gradient. This is an energy-requiring mechanism. Although early left ventricular diastolic filling is referred to as passive, myocardial relaxation is not a passive process."