NPPB and hydrops fetalis: However, thus far, none of the used biomarkers has shown proper correlation to conventional clinical or laboratory parameters of HF severity (i.e., LVEF, 6MWT, NYHA class, and NT-proBNP levels) or the ability to consistently differentiate between stable HF patients and those who will more likely deteriorate in short-, mid-, or long-term [10, 12].