['Renal function is a strong predictor of adverse events in heart failure. Current renal function measures are imperfect, and cystatin C (CysC) is promoted as a better marker of glomerular filtration rate. This study compares the prognostic use of CysC and derived glomerular filtration rate estimates with other measures of renal function in patients with chronic heart failure.', 'We measured serum CysC levels in 823 patients with heart failure undergoing coronary angiography with follow-up of major adverse cardiovascular events (death, myocardial infarction, stroke). CysC levels strongly correlated with creatinine (r=0.73), blood urea nitrogen (r=0.70), and estimated glomerular filtration rate by the 4-variable modification of diet in renal disease equation (r=-0.62) (all P<0.001). However, the correlation was lower in estimated glomerular filtration rate ≥60 mL/min per 1.73 m(2). CysC-based measures significantly improved areas under the receiver operating characteristic curve for the prediction of major adverse cardiovascular events, especially in estimated glomerular filtration rate ≥60 mL/min per 1.73 m(2) (P<0.01). Net reclassification improvement was 22.2% (P<0.001) in this group. CysC remained an independent predictor of major adverse cardiovascular events (P<0.001) after adjustment for traditional risk factors and brain natriuretic peptide.'] Does cystatin C identify patients with stable chronic heart failure at increased risk for adverse cardiovascular events?