Considering 2019–2021 as the reference period, we selected the group of patients who have been hospitalized with a primary diagnosis of HF (ICD-9 codes 428.* at discharge), with the possibility to validate it with the values of instrumental examinations, such as an echocardiogram, biomarkers (i.e., nt-proBNP) and clinical data, to render our inclusion criteria more stringent, but at the same time more confident (Figure 3). The gene discussed is NPPB; the disease is hydrops fetalis.