Risk during PTMC if the IAS is too much bulging and LA is very large. To avoid the aorta, you must puncture lower and more posterior on the fossa ovalis. The aortic root lies superior and anterior to the fossa ovalis. If LA is large, the septum bulges rightward, pushing the fossa ovalis further toward the right atrial free wall and bringing the aortic root into a precarious path if your trajectory is too superior or anterior. Puncturing lower and mid-to-posterior creates a safe clearance from the aortic root. A sharp curve made on the needle can avoid this disaster. His first position was much below the pigtail, but while pushing the needle the entire assembly jumped up and punctured aorta. Nothing happened fortunately, lower puncture was done and PTMC completed successfully with excellent split of commissures.