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Left atrial (LA) strain and strain rate, determined by speckle-tracking echocardiography (STE), are feasible and reproducible indices to assess LA function. Normal values were reported, however, technical settings might be an important source of variation.Methods: We investigated the role of gain and region of interest (ROI), as the major sources of variation when assessing LA function by STE, in 20 normal subjects (46±14 yrs, 11 men), with adequate 4C views. Longitudinal global LA strain and strain rate were assessed as the average of 6 segmental values, and strain curves were analyzed, using P-wave as a reference point. Active LA function was assessed from negative global strain at atrial contraction (GSA-), and late diastolic strain rate (GSRL); passive function from positive global strain at AVC (GSA1+), and at MVO (GSA2+), and also from early negative diastolic global strain rate (GSRE); and reservoir function from the sum of GSA- and GSA1+ (SUMGSA), and positive global strain rate at the beginning of LV systole (GSR+). All parameters were measured for different gains - minimum (G0), medium (G12), and maximum (G24), and different ROIs - minimum (ROI0), step 1 (ROI1), and 2 (ROI2).Results: Increase of gain from G0 to G24 was associated with an increase of GSA1+, GSA2+, SUMGSA, GSRE, and GSRL (all p<0.05). Increase of ROI was associated with a decrease of GSA1+, GSA2+, SUMGSA, GSRE, and GSRL (all p<0.05), with each ROI step. Gain and ROI adjustment did not change either GSA- or GSR+ (table). Conclusion: Increase of gain overestimates all LA functions. Changes in ROI width generate underestimation of LA functions, probably because of contamination by surrounding structures. These factors must be considered when using STE to define reference values for LA function. A medium gain and a minimum ROI should be used as the best choice for a correct assessment.