Concomitant cardiac and renal dysfunction has been termed the cardiorenal syndrome (CRS). This clinical condition usually manifests as heart failure with worsening renal function and occurs frequently in the acute care setting. A consistent definition of CRS has not been universally agreed upon, although a recent classification of CRS describes several subtypes depending on the primary organ injured and the chronicity of the injury. CRS may develop in adults and children and is a strong predictor of morbidity and mortality in hospitalized and ambulatory patients. The underlying physiology of CRS is not well understood, creating a significant challenge for clinicians when treating heart failure patients with renal insufficiency. This review summarizes recent data characterizing the incidence, physiology, and management of children who have heart failure and acute kidney injury.