Background: Although impaired left ventricular (LV) filling in constrictive pericarditis (CP) is attributable to external constraints by a tethered pericardium, impaired left atrial (LA) function can further impair LV filling. Previous studies focused on the impact of a tethered pericardium on LV diastolic behavior, but its impacton LA function has been largely overlooked. The objectives of this study were to evaluate LA mechanics in CP and to assess the impact of pericardiectomy on LA mechanics.Methods:A total of 52 patients with CP (mean age, 57612 years) and 19 control subjects were studiedretrospectively. All patients with CP underwent echocardiography before (median, 12 days; interquartile range,5–34 days) and after pericardiectomy (median, 20 days; interquartile range, 5–64 days). Global LA longitudinal strain (ε) was calculated, which included peak negative ε (ε negative), peak positive ε (εpositive), and the sum of those values, total LA ε(ε total), using speckle-tracking echocardiography with Velocity Vector Imaging. The regional difference of LA ε between the septal and lateral walls was assessed before and after the procedure. Results: Patients with CP showed depressed global LAεnegative,LAεtotal, and LA ε positive compared with controls. LA contractile (global LA ε negative) and reservoir functions (global LA ε total) showed significant increases after pericardiectomy. Regional analysis revealed that the improvement in LA function after surgerywas more apparent in lateral segments, while the regional function of septal walls was depressed after surgery. Conclusions: Patients with CP have impaired LA mechanics, presumably because of the constrictive tethering process involving the left atrium. Speckle-tracking echocardiography showed consistent results of changes inLA mechanics with conventional echocardiographic parameters early after the procedure. Regional ε analysis aided in recognition of the impact of constrictive tethering and pericardiectomy on LA function.