The studies reviewed in this section show that peroxynitrite can be elevated in HF and that such elevation may act to cause HF and to produce changes in SERCA2a activity, creatine kinase activity, increased nitration of tyrosine residues, increased oxidative stress, increased oxidation of β-adrenergic agents, decreased phospholamban phosphorylation and apparently increased MMPs, each of which have specific roles in HF. The gene discussed is PLN; the disease is hydrops fetalis.