Worsening renal function (WRF) during hospitalization for acute heart failure (AHF) is associated with poorer outcome. However, some studies suggest that transient WRF during treatment for AHF may not be harmful, and may even reflect a better therapeutic response . We recently showed that patients with AHF and a good diuretic response had a higher incidence of WRF but better outcomes . The cause of WRF appears to be an important factor for determining risk related to WRF. Early identification of patients at risk of WRF, as well as a robust definition and better understanding of its cause and consequences, may improve risk stratification. Novel biomarkers may play a role in achieving this goal.