Abstract Background The coexistence of hyponatremia and atrial fibrillation (AF) increases morbidity and mortality in patients with heart failure (HF). However, it is not established whether hyponatremia is related to AF or not. Objective Our study aims to seek a potential association of hyponatremia with AF in patients with reduced ejection fraction heart failure (HFrEF). Methods This observational cross-sectional single-center study included 280 consecutive outpatients diagnosed with HFrEF with 40% or less. Based on sodium concentrations ≤135 mEq/L or higher, […]