Objectives: To assess the comparative effectiveness of left atrial (LA) functional parameters (left atrial emptying fraction (LAEF), left atrial expansion index (LAi) and minimal left atrial volume index (MinLAVI)) with that of LA volume index (LAVI) in predicting heart failure (HF) and death following ST-elevated myocardial infarction (STEMI). Background: HF is common following STEMI. Enlarged LA volume as determined by echocardiography predicts adverse outcome following STEMI. However, whether echocardiographic parameters of LA function, such as LAEF, LAi and MinLAVI, are superior to LAVI for predicting prognosis following STEMI is unknown. Methods and Results: A total of 369 patients with STEMI but without atrial fibrillation or HF who were treated with primary percutaneous coronary intervention were prospectively enrolled in the period between September 2006 and December 2008. Patients underwent echocardiography shortly after STEMI. The maximal and minimal LA volumes were measured using the biplane area-length method. LAVI, MinLAVI (minimal LA volume indexed to body surface area), LAEF ((maximal LA volume–minimal LA volume)/maximal LA volume), and LAi ((maximal LA volume–minimal LA volume)/minimal LA volume) were calculated. The endpoint was a composite consisting of HF or death from any cause. During a median follow-up of 66 months (interquartile range: 50–73 months), 112 patients reached the endpoint (68 HFs, 44 deaths). Following adjustment for clinical, biochemical and echocardiographic variables, only LAEF remained an independent predictor of the composite outcome, whereas LAVI did not (LAEF: HR 1.25, P = 0.043, per 1 SD decrease) (LAVI: HR 1.01, P = 0.91, per 1 SD increase). Conclusion: In patients with STEMI who were treated with primary percutaneous coronary intervention, LAEF, as measured by echocardiography shortly after infarction, was superior to LAVI in predicting incident HF and death.