The worsening of renal function in the context of decompensated heart failure is an increasingly common clinical scenario, dubbed the cardiorenal syndrome. Its development is not completely understood; however, it results from the hemodynamic and neurohumoral alterations that occur in the setting of left ventricular pressure and volume overload with poor cardiac output. Diuretics have been the mainstay of treatment; however, they are often unsuccessful in reversing the vicious cycle of volume overload, worsening cardiac function, and azotemia. Renal replacement therapy (RRT) in the form of isolated or continuous ultrafiltration (UF) with or without a component of solute clearance (hemofiltration or hemodialysis) has been increasingly utilized as a therapeutic tool in this setting. Initial clinical trial data on the use of UF have demonstrated promising cardiac outcomes with regard to fluid removal and symptom relief without worsening renal function. The addition of a component of solute clearance may provide additional benefits in these patients with varying degrees of renal impairment. The exact clinical setting in which the various forms of RRT should be applied as initial or early therapy for acute decompensated heart failure (ADHF) remains unknown. More research examining the use of RRT in ADHF is necessary; however, it appears that the patients with the most severe clinical presentations have the best chance of benefiting from the early application of RRT.