Cardiac cycle

The sequence of contraction and relaxation events in the heart during one heartbeat. It coordinates chamber pressures, valve movements, and blood flow through the heart.

Atrial systole: The phase in which the atria contract and move blood into the ventricles. It completes ventricular filling just before ventricular contraction begins.
Cardiac conduction system: The network of specialized cardiac cells that initiates and conducts electrical impulses through the heart. Its activation sequence coordinates atrial contraction and ventricular systole.
Systolic blood pressure: The peak arterial pressure reached during ventricular contraction and ejection. It reflects pressure generated as the ventricles eject blood during systole.
Systole: The phase of the cardiac cycle when heart muscle contracts and ejects blood. It names the contraction phase, not the entire sequence of one heartbeat.
Isovolumetric contraction: Early ventricular systole, when the ventricles contract while all heart valves are closed. Rising ventricular pressure closes the atrioventricular valves before opening the outflow valves.
Electrocardiogram: A recording of electrical potential differences generated by the heart over time. Its waves provide electrical landmarks that precede mechanical events in the cycle.
Diastolic blood pressure: The lowest arterial pressure between heartbeats, during ventricular relaxation. It describes arterial pressure during the interval when the ventricles relax and fill.
Diastole: The phase of the cardiac cycle when heart muscle relaxes and chambers fill with blood. It names the relaxation phase, which alternates with systole in each cycle.
Ventricular ejection: The phase in which contracting ventricles expel blood into the pulmonary artery and aorta. It begins when ventricular pressure exceeds pressure in the great arteries.
Ventricular pressure: The force per unit area exerted by blood within a heart ventricle. Changes in ventricular pressure drive valve opening, closure, and blood ejection.

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