This patient has a type of ASD called a sinus venosus ASD, which is NOT the most common type. The labeled CT Image A shows abnormal venous return from the right upper lobe of the lung directly into the SVC, a fairly common accompanying abnormality in this condition. CT Image B shows the actual site of communication between the right atrium and left atrium. The moving images from the MR sequence C shows the same opening on a T2-weighted sequence. For the commoner type of ostium primum or ostium secundum ASD, ultrasound is usually sufficient for diagnosis, but for more complicated abnormalities, CT and MR are often needed.