in the second procedure , most of the right atrium including the sa node was excluded by an incision from the remainder of the heart , but left in continuity were the left atrium , right atrium in the area about the coronary sinus and inferior vena caval ostium and the atrial septum ( areas where the low atrial pacemakers are known to occur ) , and the ventricles .
C0018787
heart
C0225844
right atrium