An Unusual Complication of Transseptal Puncture.

The interatrial septum is a structure with complex embryological development. The true atrial septum is a circumscribed structure, and transgression outside of this area during transseptal puncture may result in entry into the extracardiac space or aorta that may result in a pericardial effusion or cardiac tamponade. (Level of Difficulty: Intermediate.).