article_snippet: the heart has two sides, separated by an inner wall called the septum.
article_snippet: The septum prevents mixing of blood between the two sides of the heart.
article_snippet: However, some babies are born with holes in the upper or lower septum.
article_snippet: A hole in the septum between the heart's two upper chambers is called an atrial septal defect (ASD).
article_snippet: A hole in the septum between the heart's two lower chambers is called a ventricular septal defect (VSD).