We describe an elderly woman with paroxysmal atrial fibrillation who was evaluated by electrocardiogram-gated multidetector-row computed tomography (MDCT) prior to left atrial radiofrequency ablation therapy to rule out coronary artery disease and to obtain a 3-dimensional anatomical map of the left atrium and pulmonary veins. MDCT documented the dynamic bidirectional motion of an interatrial septal aneurysm associated with a patent foramen ovale. MDCT findings correlated well with transesophageal and intracardiac echocardiograms.