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[[Image:Heart diastole.png|thumb|Heart during ventricular diastole.]]
'''Diastole''' ({{pron-en|daɪˈæstəli}}) is the period of time when the heart fills with blood after [[systole (medicine)|systole]] (contraction). [[Ballistics]] accurately describes diastole as [[recoil]] opposed to [[coil]] or systole.  '''[[Ventricle (heart)|Ventricular]] diastole''' is the period during which the ventricles are relaxing, while '''[[atrium (anatomy)|atrial]] diastole''' is the period during which the atria are relaxing. The term ''diastole'' originates from the Greek word ''διαστολη'', meaning dilation.<ref>[http://www.merriam-webster.com/dictionary/diastole Diastole]. Merriam-Webster Online Dictionary. 24 August 2008.</ref>

==Inside the heart==
During ventricular diastole, the pressure in the (left and right) ventricles drops from the peak that it reaches in [[Systole (medicine)|systole]].  When the pressure in the left ventricle drops to below the pressure in the left atrium, the [[mitral valve]] opens, causing accumulated blood from the atrium to flow into the ventricle. An easy way to think about this, though untrue, is that diastole is a [[sump]] that induces suction of blood into the heart to prepare for the next [[pump]] of systole.  The heart is actually filled by the momentum of the blood flowing from the previous systolic cycle, with the "atrial kick" serving as a way to "hoist" the ventricular myocardium over the mass of blood contained within the chamber just prior to systole.

The ''ventricular filling velocity'' or flow into the ventricles have two main components; First an early (''E'') diastolic one caused by accumulation of blood in the atria during previous systole, and second, a late one created by [[atrial contraction]] (''A''). The [[E/A ratio]] can be used as a diagnostic measure, since it is reduced in [[diastolic dysfunction]]. <ref>[http://www.bioline.org.br/request?mj04008] Abdul Latif Mohamed, Jun Yong, Jamil Masiyati, Lee Lim, Sze Chec Tee. ''The Prevalence Of Diastolic Dysfunction In Patients With Hypertension Referred For Echocardiographic Assessment of Left Ventricular Function.'' Malaysian Journal of Medical Sciences, Vol. 11, No. 1, January  2004, pp. 66-74</ref>

==Inside the arteries==
The adjective "diastolic" is used to refer to filling of the [[heart]] with blood between muscle contraction. It is used to describe the opposite portion of the [[cardiac cycle]] related to contraction.  More typically it is used as one component of measurement of [[blood pressure]].  "Diastolic pressure" refers to the lowest pressure within the arterial blood stream occurring during each heart beat. The other component of blood pressure is [[Systole (medicine)|systolic pressure]], which refers to the highest arterial pressure during each heart beat.

When blood pressure is stated for medical purposes, it is usually [[abuse of notation|summarized]] as a "ratio" of systolic to diastolic pressure; for example: 120/80&nbsp;[[Torr#mmHg|mmHg]].  However, this is not a true ratio: it cannot be [[Fraction (mathematics)#Equivalent fractions|reduced]] into lower terms.

==Time definition of diastole==
Time variables of diastole may be split left and right. The left heart time variable of diastole is Aortic Valve close to Aortic Valve open. The right heart time variable is Pulmonic Valve close to Pulmonic Valve open. Both are readily adapted to the [[Wiggers diagram]].

==See also==
*[[Systole (medicine)]]
*[[Blood pressure]]
*[[Wiggers diagram]]

==References==
{{reflist}}

==External links==
* {{eMedicineDictionary|Diastole}}

{{Cardiovascular physiology}}

[[Category:Cardiology]]
[[Category:Blood pressure]]
[[Category:Cardiovascular system]]

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