Background: Paediatric heart failure can be difficult to assess. Symptoms vary widely in children who have poor ventricular function on echocardiogram. In addition exercise testing is not possible in young children. BNP has been used in adult heart failure and more recently in paediatrics. We investigated BNP in the setting of a paediatric heart failure and transplantation service to assess its usefulness as a clinical marker of heart failure. Method: Clinical and echocardiographic data were correlated to 126 BNP samples. Patients were 3 weeks to 16 years of age. Left ventricular end-diastolic dimension (LVEDd) was related to normal values for body surface area (z-score). Clinical status was defined using Ross and NYHA scores. Thirty four samples were from patients with normal ventricular function. Of the remainder, most were from patients with idiopathic dilated cardiomyopathy (38), anthracycline cardiotoxicity (15), congenital heart disease (25), viral myocarditis (6) and restrictive cardiomyopathy (6). Analysis: BNP was correlated to parametric data (fractional shortening (FS%)) with pearsons correlation coefficient. For non-parametric data (z-score, NYHA and Ross score), spearmans correlation coefficient was used. Results: Rising BNP levels correlate to deteriorating clinical status with significance to the 0.01 level (Ross and NYHA), Figure 1. There was also correlation, significant to the 0.01 level to FS%, Figure 2. Increasing BNP levels correlated to the increasing LVEDd z-score significant to the 0.05 level. Mean BNP: in ventricular dysfunction 634 pg/ml (S.E.M. = 80), in normal function 11.9 pg/ml (S.E.M. = 1.6). Conclusions: This is the largest study of BNP in paediatric heart failure. The stronger correlation of BNP to NYHA and ROSS than to LVEDD and FS% suggests a useful role in assessment of children with heart failure. We believe it is useful in the outpatient setting particularly when care is shared with general paediatricians. It also appears to be a useful addition in the assessment of heart failure and perhaps timing of transplantation in a specialist centre.