Purpose. The aim of this study was to investigate the frequency with which interatrial shunts are found during routine coronary computed tomography (CT) angiography and to describe imaging characterizations of patent foramen ovale (PFO), atrial septal defect (ASD), and atrial septal aneurysm (ASA). Materials and methods. A total of 1081 adult patients were evaluated retrospectively for interatrial shunting; 77 were excluded from the study. CT diagnosis of PFO was defi ned as (1) a channel-like appearance of the interatrial septum (IAS) and (2) a contrast agent jet fl ow from the left atrium (LA) to the right atrium (RA). ASD was defi ned as (1) the IAS resembling a membrane with a hole and (2) a contrast jet fl ow between the two atria. ASA was identifi ed by detecting a minimum 10-mm protrusion of the LA beyond the IAS into the RA. Results. Among 1004 patients, 86 patients (8.6%) were diagnosed to have PFO. Another 23 patients (2.3%) had a hole in the IAS and were diagnosed as having ASD: 21 with an ostium secundum-type ASD and 2 with the sinus venosus type. ASA accompanied ASD in three patients. Conclusion. Electrocardiography-gated CT using the saline-chaser contrast injection technique that is routinely used for coronary arterial imaging can be used to detect interatrial shunts. The technique can also serve as a method for differentiating PFO, ASD, and ASA. © Japan Radiological Society 2011.