The phase of the heartbeat when the heart muscle relaxes and the chambers fill with blood, contrasting with systole (contraction).
From Greek 'dia-' (apart/through) + 'stellein' (to place/send), literally 'to separate or expand.' The term emerged in 16th-century medical terminology through anatomical study.
Your resting blood pressure number (the lower number) measures diastolic pressure—that's when your heart is relaxing and your arteries experience their lowest pressure load!
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