For a better understanding of the involvement of MMP-2 in pathological processes that lead to HF, the hearts of rats that suffered ischemia and reperfusion were evaluated, and there was an increase in the production of reactive species, including peroxynitrite (ONOO−) associated with MMP activation, before being secreted into the extracellular environment [36,49]. The gene discussed is MMP2; the disease is hydrops fetalis.