BACKGROUND Left atrial (LA) mechanics has been poorly investigated in women with subclinical hypothyroidism (SHT), and the effect of levothyroxine therapy on LA deformation and function is unknown. AIM To investigate LA phasic function and mechanics assessed by two-dimensional echocardiography (2DE) and speckle tracking in women with SHT, and to estimate the influence of levothyroxine therapy on LA remodeling. METHODS We included 48 untreated women with SHT and 38 healthy control women of the same age. All the SHT patients received levothyroxine therapy and were followed for 1 year after euthyroid status was achieved. All the participants underwent laboratory analyses and complete 2DE examination. RESULTS Left atrial total emptying fraction was significantly lower in the SHT patients at the baseline in comparison with the controls. LA passive emptying fraction gradually decreased from the controls, throughout the treated SHT patients, to the untreated SHT patients. LA active emptying fraction was lower in the controls than in the untreated and the treated SHT participants. 2DE LA longitudinal strain and systolic strain rate gradually decreased from the controls to the untreated SHT patients, whereas LA early diastolic strain rate significantly increased in the same direction. Late diastolic LA strain was lower in the controls than in the untreated and the treated SHT patients. CONCLUSION Subclinical hypothyroidism significantly affects LA mechanics. Reservoir, conduit, and booster pump LA functions are all impacted by SHT. A 1-year levothyroxine therapy significantly improves, but does not completely restore LA phasic function and mechanics in the SHT patients.