Heart failure treatment has seen great improvements in the past few decades. In many cases of heart failure, coexisting renal dysfunction, known as the cardiorenal syndrome, complicates treatment. Renal dysfunction is known to be a predictor of increased mortality. Renal dysfunction can be caused by various hemodynamic forces, medications, and intrinsic renal disease. With an understanding of the underlying etiology and physiology of the renal dysfunction, the appropriate treatment strategy can be planned. This understanding can also indicate when it is necessary to resort to therapies such as left ventricular assist device or dialysis. Such targeting of therapy can improve the prognosis of patients with heart failure and renal dysfunction.