Background Prior studies have demonstrated adverse risk associated with baseline and worsening renal function in acute heart failure, but none has modeled the trajectories of change in renal function and their impact on outcomes. Methods and Results We used linear mixed models of serial measurements of blood urea nitrogen and creatinine to describe trajectories of renal function in 1962 patients with acute heart failure and renal dysfunction enrolled in the Placebo-Controlled Randomized Study of the Selective A(1) Adenosine Receptor Antagonist Rolofylline for Patients Hospitalized with Acute Decompensated Heart Failure and Volume Overload to Assess Treatment Effect on Congestion and Renal Function study. We assessed risk of 180-day mortality and 60-day cardiovascular or renal readmission and used Cox regression to determine association between renal trajectories and outcomes. Compared with patients alive at 180 days, patients who died were older, had lower blood pressure and ejection fraction, and higher creatinine levels at baseline. On average for the entire cohort, creatinine rose from days 1 to 3 and increased further after discharge, with the trajectory dependent on the day of discharge. Blood urea nitrogen, creatinine, and the rate of change in creatinine from baseline were the strongest independent predictors of 180-day mortality and 60-day readmission, whereas the rate of change of blood urea nitrogen from baseline was not predictive of outcomes. Baseline blood urea nitrogen >35 mg/dL and increase in creatinine >0.1 mg/dL per day increased the risk of mortality, whereas stable or decreasing creatinine was associated with reduced risk. Conclusions Patients with acute heart failure and renal dysfunction demonstrate variable rise and fall in renal indices during and immediately after hospitalization. Risk of morbidity and mortality can be predicted based on baseline renal function and creatinine trajectory during the first 7 days. Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifiers: NCT00328692 and NCT00354458.