NPPB and atrial septal defect: Second, the different study design, disease type and cut-off of both BNP and NT-proBNP were not the cause of heterogeneity (p > 0.05); however, paediatric structural cardiac diseases, like atrial septal defects, ventricular septal defects, etc., could both cause PH and an increase in BNP/NT-proBNP, videlicet increased BNP/NT-proBNP might be related to the altered cardiac structures and not necessarily be related to PH.