© 2014 The Authors. European Journal of Heart Failure published by John Wiley & Sons Ltd on behalf of European Society of Cardiology. Aims Worsening heart failure (WHF) in the first 7 days after an admission for acute HF (AHF) has been proposed as a therapeutic target in several recent AHF studies and was a co-primary endpoint of the VERITAS studies.Methods and results Patients were randomized within 24 h of admission for AHF. WHF was defined as worsening or persistent signs and symptoms of HF requiring additional intravenous or mechanical therapy for HF or death within 7 days of randomization. Multivariable models were developed to predict the time to WHF through day 7. Unadjusted and multivariable-adjusted associations of WHF with the length of stay (LOS) of the index hospitalization, and 30- and 90-day outcomes were estimated. WHF occurred by day 7 in 27% of the 1347 patients enrolled. Age, co-morbidities, and markers of HF severity were moderately predictive of WHF; the C-index for a multivariable model for WHF was 0.66. After multivariable adjustment for baseline characteristics, WHF was associated with an increase in LOS of 4.33 days [95% confidence interval (CI) 3.54-5.13 days], a hazard ratio (HR) for 30-day HF readmission or death of 2.43 (95% CI 1.75-3.40), and a HR for 90-day mortality of 2.57 (95% CI 1.81-3.65), all with P < 0.0001.The associations of WHF with these outcomes remained largely unchanged after adjustment for both baseline characteristics and changes in markers of renal and hepatic dysfunction during the first day of admission.Conclusions In patients admitted for AHF, WHF is a significant clinical event that is associated with delays in discharge and higher rates for readmission and death.