Left atrial (LA) remodeling has been identified to predict atrial fibrillation (AF) and heart failure. However, the role of LA diameter (LAD) in patients with heart failure (HF) with preserved (HFpEF), mid-range (HFmrEF), and reduced ejection fraction (HFrEF) remains poorly understood.A total of 142 patients including 71 subjects with AF (21 of HFpEF, 22 of HFmrEF, and 28 of HFrEF) and 71 ejection fraction (EF)-matched subjects with sinus rhythm (SR) were included in the study. Baseline characteristics and echocardiographic parameters including LAD were compared between both groups as well as among HFpEF, HFmrEF, and HFrEF.In receiver-operating characteristic (ROC) analyses, LAD predicted AF in HFpEF, HFmrEF, and HFrEF [area under the curve (AUC): 0.646; P = .03]. LAD was negatively association with left ventricular ejection fraction while positively with Nt-proNP and left ventricular end-diastolic diameter (regression coefficient: -0.239, P = .004; regression coefficient: 0.191, P = .023; regression coefficient: 0.357, P < .001). In ROC analyses, LAD predicted HFrEF among the 3 categories (AUC: 0.629, P = .01).In the setting of HF, LAD was higher in AF than in and SR, and predicted AF. Furthermore, LAD was associated with severity of HF in HFpEF, HFmrEF, and HFrEF, and also predicted HFrEF.