Most patients with heart failure have mild or moderate renal dysfunction. This reflects the combined impact of chronic renal parenchymal disease, renal artery disease, renal congestion and hypoperfusion, neuroendocrine and cytokine activation and the effects of treatments for heart failure. Remarkably, with good treatment, the average annual rate of decline in renal function is similar in patients with chronic heart failure and healthy people of a similar age. Urea appears to be a stronger marker of an adverse prognosis than creatinine-based measures of renal function. Recent evidence suggests that minor, transient increases in creatinine in the setting of acute heart failure are not prognostically important but persistent deterioration does indicate a higher mortality. The poor prognosis of patients with worsening renal function ensures that few require renal dialysis but this may change as methods to prevent sudden death improve and new ways are found to control fluid congestion. Reversing renal dysfunction and stopping its progression remain important targets for treatment of heart failure.