Balloon septostomy is the widening of a foramen ovale, patent foramen ovale (PFO), or atrial septal defect (ASD) via cardiac catheterization (heart cath) using a balloon catheter.

This procedure allows a greater amount of oxygenated blood to enter the systemic circulation in some cases of cyanotic congenital heart defect (CHD).

This is normally a palliative procedure used to prepare a patient for, or sustain them until, a corrective surgery can be performed.

At this time the ASD is closed using either sutures or a cardiac patch, depending on the size and/or nature of the opening.

The procedure is often unsuccessful in infants and children older than one month because of a thickened septum.