Clinical diastole is from the point of aortic valve closure to the point of mitral valve closure. But actual relaxation of the ventricle starts prior to that.

Diastole is both passive as well as an active process and needs adenosine triphosphate (ATP) for:

-release of calcium from Troponin C

-reuptake of calcium into sarcoplasmic reticulum (SR) by Sarco/Endoplasmic Reticulum Ca2+ ATPase (SERCA)

-extrusion of calcium from cytoplasm

Diastolic relaxation property is known as lusitropy

Diastole has four components: isovolumic relaxation, rapid filling, slow filling or diastasis and atrial contraction. Atrial kick accounts for 20% of ventricular filling in normal individuals, but is increased in diastolic dysfunction, but seldom above 50%.

If the ventricle can accommodate an extra preload without increasing the filling pressures, the diastolic function is good.