#atrium.chamber  any chamber that is connected to other chambers or passageways (especially one of the two upper chambers of the heart)
  supertype:  chamber.bodily_cavity  an enclosed volume (as the aqueous chamber of the eyeball or the chambers of the heart)
  subtype:  atrium_cordis__atrium_of_the_heart  the upper chamber of each half of the heart
     subtype:  right_atrium_of_the_heart__right_atrium__rightatrium__atrium_dextrum  the right upper chamber of the heart that receives blood from the venae cavae and coronary sinus
     subtype:  left_atrium_of_the_heart__left_atrium__atrium_sinistrum  the left upper chamber of the heart that receives blood from the pulmonary veins

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