MPO activity (in both cases: ↑72.72%, p < 0.0001) and nitrotyrosine concentration (↑83.04%, p = 0.0039; ↑88.08%, p = 0.0044, respectively) were statistically significantly higher in the groups of HF patients with NS, as well as HS, compared to the controls, while the content of S-nitrosothiols (↓78.45%, p = 0.0008; ↓75.96%, p < 0.0001, respectively) was markedly lower. This evidence concerns the gene MPO and hydrops fetalis.