Background: Patent foramen ovale (PFO) is associated with various diseases such as cryptogenic stroke, migraine, and platypnea–orthodeoxia syndrome. This study aimed to evaluate the diagnostic performance of cardiac computed tomography (CT) for PFO detection. Materials and Methods: Consecutive patients diagnosed with atrial fibrillation and who underwent catheter ablation with pre-procedural cardiac CT and transesophageal echocardiography (TEE) were enrolled in this study. The presence of PFO was defined as (1) the confirmation of PFO using TEE and/or (2) the catheter crossing the interatrial septum (IAS) into the left atrium during ablation. CT findings indicative of PFO included (1) the presence of a channel-like appearance (CLA) on the IAS and (2) a CLA with a contrast jet flow from the left atrium to the right atrium. The diagnostic performance of both a CLA alone and a CLA with a jet flow was evaluated for PFO detection. Results: Altogether, 151 patients were analyzed in the study (mean age, 68 years; men, 62%). Twenty-nine patients (19%) had PFO confirmed by TEE and/or catheterization. The diagnostic performance of a CLA alone was as follows: sensitivity, 72.4%; specificity, 79.5%; positive predictive value (PPV), 45.7%; negative predictive value (NPV), 92.4%. The diagnostic performance of a CLA with a jet flow was as follows: sensitivity, 65.5%; specificity, 98.4%; PPV, 90.5%; NPV, 92.3%. The diagnostic performance of a CLA with a jet flow was statistically superior to that of a CLA alone (p= 0.045), and the C-statistics were 0.76 and 0.82, respectively. Conclusion: A CLA with a contrast jet flow in cardiac CT has a high PPV for PFO detection, and its diagnostic performance is superior to that of a CLA alone.