And this condition is known as the patent for Raymond, or valley, and it is the most common type of atrial septal defect. Now, what exactly is an atrial septal defect? Well, septal simply means wall. The atria is referring to those two chambers of the heart, and a defect means it's an abnormality. So normally, it closes. But in this type of defect, we have some type of abnormality that causes this valve to actually remain open.