N-terminal pro-brain natriuretic peptide (NT-proBNP) may be useful in the diagnosis of heart failure and ventricular dysfunction. Obesity is an independent cardiovascular risk factor. The purpose of this study was to measure NT-proBNP plasma levels in obese and non-obese subjects with heart failure and to compare levels in subjects with ischaemic and dilated aetiology. In this study, obese subjects had 63% lower NT-proBNP plasma levels than non-obese subjects (p < 0.01). In multivariate analysis, BMI was inversely associated with NT-proBNP plasma levels (p < 0.05) and a 17% decrease in natriuretic peptide levels was attributed to obesity (p < 0.036). When we analyzed data according to the aetiology of heart failure, we found that both groups (ischaemic and dilated) had a 65% decrease in NT-proBNP plasma levels in obese subjects compared to non-obese subjects.