Background: The prognostic value of LA functional measures in heart failure patients with reduced ejection fraction (HFrEF) is unclear. Therefore, this study investigated the prognostic value of left atrial (LA) functional measures such as the left atrial emptying fraction (LAEF) and the minimal LA volume compared with left atrial volume index (LAVI) in HFrEF patients. Methods and Results: A total of 818 HFrEF patients with left ventricular ejection fractions <45% underwent echocardiography. LA volumes were determined by the area-length method from the apical 2-chamber and apical 4-chamber views. LAEF, minimal LA volume indexed to body surface area (MinLAVI), and LAVI were calculated. The end point was all-cause mortality. During a median follow-up of 3.3 years (interquartile range 1.8–4.6 years), 121 patients died (14.8%). Follow-up was 100%. In a final multivariable model adjusting for clinical and echocardiographic parameters, LAEF, but not MinLAVI or LAVI, was an independent predictor of all-cause mortality in HFrEF patients: LAEF: hazard ratio (HR) 1.11 (P =.033) per 5% decrease; MinLAVI: HR 1.03 (P =.57) per 5 mL/m ² increase; LAVI: HR 1.06 (P =.16) per 5 mL/m ² increase. Conclusions: LAEF is an independent predictor of all-cause mortality in HFrEF patients after multivariable adjustment. LAEF provides incremental prognostic value over LAVI in risk stratification of HFrEF patients.