TLR9 and hydrops fetalis: Of the 52 animals in the combined survival study (WT, n = 7; TLR9 KO, n = 3; SERCA2a KO, n = 22; and SERCA2a/TLR9 KO, n = 20), 16 animals were euthanized due to objective prespecified criteria of distress (see Table S1) indicating severe HF (SERCA2a KO, n = 6; SERCA2a/TLR9 KO, n = 10) and 26 animals died spontaneously (SERCA2a KO, n = 16; SERCA2a/TLR9 KO, n = 10).