Cardiac Cycle: Systole and Diastole
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The cardiac cycle alternates systole, when heart chambers contract and eject blood, with diastole, when chambers relax and refill, repeating continuously to maintain circulation.
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Blood pressure readings report systolic pressure over diastolic pressure, capturing both phases of a single cycle.
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Atria and ventricles do not contract simultaneously — atrial contraction slightly precedes ventricular contraction within each cycle.