NPPA and hydrops fetalis: Among the various factors hampering this, such as a shorter half-life, the most important is most likely the higher complexity of the endocrine function of the atria combined with several unresolved questions in the available literature regarding the mechanism of regulation during different diseases (such as HF and AF), the presence of a specific site for ANP secretion, the specific interplay between filling pressure, atrial contraction, and the presence of fibrosis.