NPPB and hydrops fetalis: Beyond mechanisms of renal resistance to NPs, the BNP paradox in HF is defined as alterations in physiological responses (e.g., increased vasoconstriction, decreases in diuresis, natriuresis, urinary cGMP excretion) resulting in clinical aggravation, despite a significant increase in BNP plasma levels using standard immunoreactive assay kits [87].