NPPA and heart failure: ANP is secreted by cardiomyocytes in response to cardiac stretch of the atria.17 ANP can indicate left ventricular volume overload in children with heart failure.18 In very preterm infants, MR-proANP was associated with the presence of hsPDA.19 Also, Gerull et al. found that MR-proANP (as well as CT-proET1) serve as early markers of respiratory morbidity.13 In comparison, Endothelin-1 is released by endothelial cells in response to sheer stress and hypoxaemia.