Findings demonstrate the usefulness of serum chloride level in predicting poor outcome in acute decompensated heart failure (ADHF) patients with preserved ejection fraction.

• Data from a prospective multicenter observational registry were selected for 870 patients to clarify the link between serum chloride level and clinical results in patients with heart failure with preserved ejection fraction with ADHF.

• At discharge, right ventricular systolic dysfunction was found to be significantly linked with the lowest tertile of serum chloride level post-multivariable adjustment.

• In Cox multivariable analysis, an independent association was found between serum chloride level at discharge and all-cause mortality post-multivariable adjustment of major confounders, whereas serum sodium level was no longer significant.

• Kaplan–Meier survival curve analysis demonstrated a significantly elevated risk of mortality stratified by the tertile of serum chloride concentration [29% vs 19% vs 16%, P = 0.0002; hazard ratio (HR): 2.09 (95% confidence interval, CI: 1.31 to 3.34), HR: 1.03 (95% CI: 0.65 to 1.64)].