Isovolumetric relaxation

Filling Isovolumetric contraction Ejection Isovolumetric relaxation... 

As the muscle begins to relax, pressure will drop until it falls below the aortic pressure. At this time, the aortic valve closes, and again blood flow ceases. Meanwhile, the ventricle continues to relax, decreasing the ventricular pressure. This period (D to A) is termed isovolumetric relaxation. Here, muscle relaxation can be thought of as increasing the compliance of the chamber. Finally, ventricular pressure falls below atrial pressure, the mitral valve opens, and the cycle begins anew. 

BACH et al. 2000, Lu et al. 2001 Husmann et aL 2007). During isovolumetric relaxation at mid-diastole and during mid- to late systole, coronary motion is relatively quiescent. With increasing heart rates, the minimum mid diastolic velocity increases, while the width of the mid-diastolic velocity trough successively decreases and eventually disappears. At heart rates greater than approximately 80 bpm, the lowest velocities in systole are lower than the lowest velocities in diastole. 

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