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Cardiac Cycle

Ventricular Filling Period
First phase of the cardiac cycle and during part of the diastole phase. Lasts around 0.5
seconds. The pressure difference between the left ventricle and atria causes the atrioventricular
(mitral, tricuspid) valves to open. The ventricles begin to passively fill with blood from the atria.
Once the ventricles are 70-80% filled, the atria contract causing the remainder of the blood to fill
the ventricles.
Isovolumetric Contraction Period
At the beginning of the systole phase. Lasts around 0.05 seconds. All valves of the heart
are closed during this phase. Ventricular contraction causes the ventricles to have an increase
in pressure. When the pressure of the left ventricle is greater than that of the aorta, the
semilunar valves (aortic, pulmonary) open starting the next phase.
Ventricular Ejection Period
Makes up the majority of the systole phase, lasting around 0.3 seconds. Blood is ejected
from the ventricles to the rest of the body as the semilunar valves open. The ventricular volume
decreases rapidly.
Isovolumetric Relaxation Period
At the beginning of the diastole phase, but the last phase of the cardiac cycle. Lasts
around 0.08 seconds. The ventricles relax as the pressure decreases. When the ventricular
pressure is lower than that of the aorta, all valves of the heart are closed. The atria fill with blood
until the atrial pressure is larger than the ventricular pressure. Once that happens the AV valves
open, causing the cycle to begin again.