Diastole
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Diastole is the period of time when the heart relaxes after contraction. Ventricular diastole is when the ventricles are relaxing, while atrial diastole is when the atria are relaxing.
During ventricular diastole, the pressure in the (left and right) ventricles drops from the peak that it reaches in systole. When the pressure in the left ventricle drops to below the pressure in the left atrium, the mitral valve opens, and the left ventricle fills with blood that was accumulating in the left atrium.
Diastolic is the adjective form of diastole referring to relaxation of the heart, between muscle contractions.
As such, it is used to describe portions 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 systolic pressure, which refers to the highest arterial pressure during each heart beat.
