['We studied prevalence, causes and consequences of worsening renal function (WRF) during hospitalization for acute heart failure (AHF).', 'Patients admitted for AHF were enrolled. Patients with severe chronic renal failure, cardiogenic shock and contrast medium-induced nephropathy were excluded. WRF was defined as an increase of 25 mumol/l or more in serum creatinine relative to the admission level. Survivors were monitored for 6 months, focusing on deaths and first unscheduled readmissions for heart failure.', 'Among the included 416 patients, WRF occurred in 152 cases (37%), 5+/-3 days after admission, and two-thirds of patients recovered their baseline renal function before discharge. Old age, diabetes, hypertension and acute coronary syndromes increased the risk of WRF. In-hospital furosemide doses as well as discharge treatment were similar in WRF and no-WRF patients. Serum creatinine elevation was the strongest independent determinant of a longer hospital stay (r=0.37, p=0.001). Adverse events occurred in 158 patients (38%) during follow-up, with 23 deaths and 135 readmissions. Cox analysis showed that WRF, transient or not, was an independent predictor of the risk of death or readmission (hazard ratio=1.74 [1.14-2.68], p=0.01).'] Does transient worsening of renal function during hospitalization for acute heart failure alter outcome?