['Pectus excavatum is a skeletal abnormality that may have cardiac manifestations.', 'To determine whether pectus excavatum is associated with lone atrial fibrillation (AF).', 'The pectus severity index (PSI) is the ratio of the lateral diameter of the chest to the distance between the sternum and the spine on computed tomography scan. A normal PSI is ≤2.5 whereas patients with severe pectus excavatum have a PSI >3.25. We calculated the PSI of 220 consecutive patients with AF who underwent radiofrequency catheter ablation from September 2008 to 2012 and compared this to the PSI of 225 controls without a history of AF undergoing chest computed tomography.', 'Mean PSI was higher in patients with lone AF (2.72 ± 0.07) compared to patients with nonlone AF (2.25 ± 0.03) or controls (2.26 ± 0.03) (P < .001). The likelihood of mild, moderate, or severe pectus excavatum was higher in patients with lone AF compared to patients with nonlone AF and controls (P < .001). Patients with lone AF were more than 5 times as likely to have severe pectus excavatum compared to patients with nonlone AF or controls (P < .001) even after adjustment for potential confounders.'] Is lone atrial fibrillation associated with pectus excavatum?