Every child is born with an opening between the upper chambers of the heart. It's a normal fetal opening that enables blood to deviate from the lungs before birth. After birth, the opening is no longer required and generally closes or becomes small within a few weeks or months. Sometimes the opening is larger than ordinary and does not close after birth. The cause is not recognized in most children. Some kids may have other heart conditions along with ASD. If the ASD is large, it can be shut by open-heart surgery or by cardiac catheterization employing a device implanted into the opening to plug it in. Sometimes if the ASD is in an uncommon position within the heart, or if there are other cardiac defects, such as irregular vein connections that bring blood back from the lungs to the heart (pulmonary veins), the ASD cannot be closed with the catheter technique. After that, treatment is required.