Substrates for neprilysin include NPs (kinetic affinity CNP = ANP > BNP) [5], angiotensin, adrenomedullin, substance P, etc. The inhibition of neprilysin prolongs the half-life of endogenous natriuretic peptides together with angiotensin II, so the co-inhibition of RAAS was required for therapeutics in HF. Here, NPPB is linked to hydrops fetalis.