Patients with acute coronary syndrome (ACS) have a high incidence of Left ventricle diastolic dysfunction (DD). Latest algorithms for the assessment of DD lay on 2D parameters and describe a grading to quantify its severity. However, there persists a "gray zone" of values in which DD remains indeterminate. to analyze the diagnostic value of Left atrium strain (LAS) for categorization of LV DD and assessment of LV filling pressures in ACS patients. Cross-sectional study that prospectively evaluated 105 patients presenting ACS with preserved LV ejection fraction (LVEF). Patients were divided in 4 groups according to the DD grade. Mean values of LAS, corresponding to three phases of atrial function: reservoir (LASr), conduit (LAScd) and contraction (LASct), were obtained by speckle-tracking echocardiography. Mean age was 60±10 years, with a gender ratio of 6.14. LASr and LASct were significantly lower according to DD severity (p combined=0.021, p combined=0.034; respectively). E/e' ratio was negatively correlated to LASr (r= - 0.251; p= 0.022) and LASct (r= -0.197; p=0.077). Left atrial volume index (LAVI) was also negatively correlated to LASr (r= -0.294, p= 0.006) and LASct (r= -0.3049, p=0.005). Peak tricuspid regurgitation was negatively correlated to LASr (r=-0.323, p=0.017) and LASct (r=-0.319, p=0.020). Patients presenting elevated LV filling pressures had lower LASr and LASct (p=0.049, p=0.022, respectively) compared to patients witn normal LV filling pressures. ROC curve analysis showed that a LASr < 22% (Se= 75%, Sp= 73%) and a LASct < 13% (Se= 71%, Sp=58%) can increase the likelihood of DD grade II or III by 4.6 (OR= 4.6; 95% CI: 1.31-16.2; p=0.016) and 3.7 (OR= 3.7; 95% CI: 1.06-13.1; p= 0.047), respectively. LAS is a valuable tool, which can be used to categorize DD in ACS patients.