B-type natriuretic peptide (BNP) was measured in 43 children and adolescents with high-grade second degree or complete atrioventricular conduction block. BNP plasma level was significantly higher (p<0.01) in patients without pacemaker (n=21) than in patients with permanent pacemaker (n=26). In all four patients with measurement of BNP both before and after placement of a permanent pacemaker, individual plasma BNP decreased. Additionally, patients with dual-chamber pacing had significantly lower BNP values compared to those with single chamber ventricular pacing (p<0.05). Conclusively, high degree atrioventricular block can induce elevated plasma BNP levels and the loss of atrioventricular synchrony induce a further increase of plasma BNP.