Definition of Septum, heart

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Septum, heart: The septum of the heart is the dividing wall between the right and left sides of the heart.

That portion of the septum that separates the two upper chambers (the right and left atria) of the heart is termed the atrial (or interatrial) septum while the portion of the septum that lies between the two lower chambers (the right and left ventricles) of the heart is called the ventricular (or interventricular) septum.

The word "septum" is borrowed from the Latin "saeptum" meaning a "dividing wall or enclosure."