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Background: The 6-min walk test (6-MWT) may serve as a simple clinical tool to assess functional capacity in patients with heart failure. The aim of this study was to identify cardiac functional parameters which predict 6-MWT measures of exercise capacity in patients with systolic heart failure.Methods: In 231 patients (mean age 61.6±10 years, 51.5% male) with clinical diagnosis of congestive heart failure (NYHA: 2.25±0.7). A 6-MWT and an echo-Doppler study were performed in the same day. Left ventricular (LV) end-diastolic (EDD) and end-systolic (ESD) dimensions, fractional shortening (FS), ejection fraction (EF) and E:A ratio, were measured. Restrictive filling was defined as E:A ratio >1.5 and E-wave deceleration <140ms. LV long axis function was studied using M-mode (amplitude) and tissue Doppler (myocardial velocities). LV dyssynchrony was indirectly assessed by total isovolumic time - t-IVT [in s/min; calculated as: 60 – (total ejection time – total filling time)], and Tei index (t-IVT/ejection time). Patients were divided into two groups based on the 6-MWT distance (Group I: ≤300m, and Group II: >300m).Result: Group I patients were older (p=0.008), had higher blood urea and creatinine levels (p=0.026, and p=0.038, respectively), higher NYHA class (p=0.002), lower EF (p=0.021), longer t-IVT (p< 0.001) and higher Tei index (p<0.001), compared with Group II patients. In multivariate analysis, only age [0.798 (0.640-0.994), p=0.044], and t-IVT [0.528 (0.316-0.882), p=0.015] independently predicted poor 6-MWT performance (<300m).Conclusion: In patients with systolic heart failure apart from age, LV dyssynchrony is the only cardiac functional predictor of exercise capacity.