Abstract Background Left atrial stiffness index (LASI) derived from speckle-tracking echocardiography (STE) is a marker of pressure transfer to the pulmonary circulation and a predictor of symptoms in patients with heart failure (HF). However, the role of the right atrial stiffness index (RASI) in the setting of left-sided HF is incompletely understood. Purpose We sought to evaluate the left, right and combined bi-atrial stiffness index (BASI) in a cohort of patients with dilated cardiomyopathy (DCM) and to assess their prognostic role. Methods We prospectively enrolled 60 consecutive patients with DCM in sinus rhythm, who underwent transthoracic echocardiography. As previously described, LASI was defined as the ratio between early diastolic transmitral flow velocity/lateral mitral annulus myocardial velocity (E/e') and left atrial reservoir strain derived from STE. RASI was defined as the ratio between early diastolic tricuspid flow velocity/lateral tricuspid annulus myocardial velocity (Et/e't) and right atrial reservoir strain. BASI was defined as the sum of LASI and RASI. Patients were followed for 19±9 months for an endpoint of HF decompensation requiring hospitalization. Results 29 patients reached the endpoint. Patients with rehospitalization had higher LASI (2.50±2.15 vs. 1.23±1.61, p=0.01), higher RASI (0.76±0.77 vs. 0.36±0.41, p=0.02) and higher BASI (3.25±2.65 vs. 1.59±1.71, p=0.006). In univariate Cox regression, all three stiffness indices were predictors of adverse outcome: HR=2.63 [95% CI, 1.22–5.66], p=0.014 for LASI, HR=2.86 [95% CI, 1.26–6.48], p=0.012 for RASI, HR=3.49 [95% CI, 1.49–8.20], p=0.004 for BASI. A multivariable model was constructed using well-established event predictors in DCM. After adjustment for age, left ventricular ejection fraction and indexed maximal left atrial volume, BASI was the only stiffness index that remained an independent predictor of rehospitalization for HF: HR=2.76 [95% CI, 1.08–7.03], p=0.03. In ROC analysis, a BASI greater than 1.25 had a 75.9% sensitivity and 64.5% specificity for event prediction (AUC=0.716, p=0.004). Conclusion Stiffness of both atria is significantly greater in patients with DCM who get hospitalized for HF decompensation. Combining the left and right atrial stiffness indices provides a better prognostic stratification than left or right atrial stiffness alone, since BASI was the only stiffness index that remained an independent predictor of rehospitalization after adjustment for confounders. Funding Acknowledgement Type of funding sources: None.