Diastole

The term originates from the Greek word διαστολή (diastolē), meaning "dilation",[1] from διά (diá, "apart") + στέλλειν (stéllein, "to send").

A typical heart rate is 75 beats per minute (bpm), which means that the cardiac cycle that produces one heartbeat, lasts for less than one second.

The open mitral valve allows blood in the atrium (accumulated during atrial diastole) to flow into the ventricle (see graphic at top).

After chamber and back pressures equalize, the mitral and tricuspid valves open, and the returning blood flows through the atria into the ventricles.

[10] Classification of blood pressure in adults:[11] Brain natriuretic peptide (BNP) is a cardiac neurohormone secreted from ventricular myocytes (ventricular muscle cells) at the end of diastole—this in response to the normal, or sub-normal (as the case may be), stretching of cardiomyocytes (heart muscle cells) during systole.

Elevated levels of BNP indicate excessive natriuresis (excretion of sodium to the urine) and decline of ventricular function, especially during diastole.

[12] Impaired diastolic function can result from the decreased compliance of ventricular myocytes, and thus the ventricles, which means the heart muscle does not stretch as much as needed during filling.

Over time, decreased cardiac output will diminish the ability of the heart to circulate blood efficiently throughout the body.

Early ventricular diastole is the filling of blood from the atria (from the left atrium shown in pink, and from the right atrium shown in blue) that weakly contract letting blood fill into the ventricles; in late ventricular diastole, the two atria begin to contract (atrial systole), forcing additional blood flow into the ventricles.
A Wiggers diagram , showing various events during diastole. During early ventricular diastole —see vertical bar marked "Isovolumetric relaxation"—pressure in each ventricle (light-blue trace) begins to drop quickly from the wave height reached during systole. When ventricular pressures fall below those in the atrial chambers the atrioventricular (mitral and tricuspid) valves open, causing blood volume (red trace) in the atria to flow into the ventricles.  In late ventricular diastole , the two atrial chambers begin to contract ( atrial systole ), causing blood pressure in both atria to increase and forcing additional blood volume into the ventricles. This beginning of the atrial systole is known as the atrial kick—see "Ventricular volume" trace (red) directly above the P-wave in the electrocardiogram trace (dark-blue).