Abstract Aims Little is known about the relative importance of body volume and haemodynamic parameters in the development of worsening of renal function in acutely decompensated heart failure (ADHF). To study the relationship between haemodynamic parameters, body water content and worsening of renal function in patients with heart failure with reduced ejection fraction (HFrEF) hospitalised for ADHF. Methods and results This prospective observational study involved 51 consecutive patients with HFrEF (age: 73±14 years, male: 60%, left ventricular ejection fraction: 33.3%±9.9%) hospitalised for ADHF. Echocardiographic-determined haemodynamic parameters and body volume determined using a bioelectric impedance analyser were serially obtained. All patients received intravenous furosemide 160 mg/day for 3 days. There was a mean weight loss of 3.95±2.82 kg (p<0.01), and brain natriuretic peptide (BNP) reduced from 1380±901 pg/mL to 797±738 pg/mL (p<0.01). Nonetheless serum creatinine (SCr) increased from 134±46 μmol/L to 151±53 μmol/L (p<0.01), and 35% of patients developed worsening of renal function. The change in SCr was positively correlated with age (r=0.34, p=0.017); and negatively with the ratio of extracellular water to total body water, a parameter of body volume status (r=−0.58, p<0.001); E:E’ ratio (r=−0.36, p=0.01); right ventricular systolic pressure (r=−0.40, p=0.009); and BNP (r=−0.40, p=0.004). Counterintuitively, no correlation was observed between SCr and cardiac output, or total peripheral vascular resistance. Regression analysis revealed that normal body volume and lower BNP independently predicted worsening of renal function. Conclusions Normal body volume and lower serum BNP on admission were associated with worsening of renal function in patients with HFrEF hospitalised for ADHF.