Diastole

Diastole /daɪˈæstəliː/ is the part of the cardiac cycle when the heart refills with blood following systole (contraction). Ventricular diastole is the period during which the ventricles are filling and relaxing, while atrial diastole is the period during which the atria are relaxing. The term diastole originates from the Greek word διαστολη, meaning dilation. Diastole is closely related to the phenomenon of recoil within ballistics.

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, causing accumulated blood from the atrium to flow into the ventricle.

The ventricular filling velocity or flow into the ventricles have two main components; First an early (E) diastolic one caused ventricular suction, 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.

Early diastole, i.e., the E-wave in the E/A ratio, is a suction mechanism. In late diastole, i.e., the A-wave, as the left and right atria contract, the blood pressure in each atrium increases, forcing additional blood into the ventricles. This is known as atrial kick. 80% of the blood flows passively down to the ventricles during the E-wave active suction period, so the atria do not have to contract a great amount.

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