Brain natriuretic peptide (BNP) levels were obtained before cardiac catheterization in 193 pediatric patients with a variety of cardiac lesions. Age and functional status had strong relations to BNP values, with elevations of BNP levels associated with increasing functional disability and decreasing age. Mild but statistically significant correlations were found between BNP levels and right-sided cardiac pressures. In patients with volume-overloaded ventricles, BNP correlated with the degree of overcirculation.