The electrical event that immediately precedes blood being ejected to the pulmonary trunk / aorta is called ventricular systole
The pressure of the blood inside the ventricle initially increases when its muscles contract, but it is still too low for the semilunar (pulmonary and aortic) valves to open and allow blood to exit the heart. The blood pressure, however, quickly exceeds that of the atrium, which is now relaxed and in diastole. The tricuspid and mitral valves close as a result of the blood flowing back into the atria as a result of the pressure increase. The amount of blood inside the chamber stays constant since blood is not yet being expelled from the ventricles. called ventricular systole As a result, the term "isovolumic contraction," sometimes known as "isovolumetric contraction," refers to this early stage of ventricular systole.
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