incision into an anatomical partitions (a septum) to create passage between two adjacent cavities.
eg. atrial septotomy
procedure to allow oxygenated and non oxygenated blood mix in the heart atria to temporarily improve blood oxygen levels prior to repair of congenital pulmonary artery and vein heart defect (oxygenated blood is not properly circulated past the lungs).
during heart surgery the septotomy will be repaired after the blood vessels are surgically placed in their correct anatomical positions.
below: a congenital septal defect.