CD8A and hydrops fetalis: Given that T cell activation significantly contributes to the development of HF (9, 11, 19–21), and the important role of CD8+ T cells in modulating inflammatory responses in various diseases, we investigated the role of CD8+ T cells in HF progression in mice with preexisting LV failure, and their role in the exacerbated LV dysfunction in mice after depletion of Tregs.