Many studies have shown that the B-type natriuretic peptides (BNP and NT-proBNP) are proven diagnostic markers for heart failure due to left ventricular systolic dysfunction. The manner in which they are to be used is still being unravelled; most single centre studies have chosen the best concentration of the peptide on ROC analysis as their cut-point resulting in numerous different values for both BNP and NT-proBNP appearing in the literature. We report a different approach of defining an age and sex corrected abnormal concentration for NT-proBNP, derived from normal individuals within a large sample of 3051 subjects pooled from three European epidemiology studies and applying that to the entire population to detect HF and LVD. Three thousand and fifty one subjects were studied. Of these 10% (305) had significant LVD and 3.1% (94) had HF. The median concentrations of NT-proBNP (IQR) in normals, those with LVD and in heart failure subjects were 20 pg/ml (10.30), 117.3 pg/ml (28.145) and 269.6 pg/ml (54.323), P<0.001, respectively. The area under the ROC curve for NT-proBNP for the detection of 'heart failure' was 0.85 and 0.69 for LVD. NT-proBNP was an independent predictor of the presence of HF on multivariate analysis. An abnormal NT-proBNP was defined as being >95th centile for normals, age and sex corrected, and diagnosed HF with a sensitivity of 75% and a negative predictive value of 99%. In an additional analysis in a breathless subgroup of our population, in 30% a raised NT-proBNP concentration could be explained by HF due to LVD, in another 64% the high BNP level was associated with some other structural of functional cardiac abnormality or renal impairment. We were unable to assign a possible cause to the high NT-proBNP values in 5.9% of this breathless subgroup of the population. An abnormal NT-proBNP concentration is an accurate diagnostic test both for the exclusion of HF in the population and in ruling out LVD in breathless subjects. An elevated NT-proBNP merely indicates the presence of 'cardio-renal distress' and should prompt referral for further investigation.