SOD2 and congestive heart failure: E2: estrogen or 17B-estradiol; EXD: Er-Xian Decoction; Trx: thioredoxin; MnSOD: manganese superoxide dismutase; OVX: ovariectomized rats; GPER: G-protein coupled estrogen receptor; ROS: reactive oxygen species; CHF: congestive heart failure; mRNA: messenger ribonucleic acid; NADPH: nicotinamide adenine dinucleotide phosphate; p38β: mitogen-activated protein kinase; c-fos mRNA: cell activation marker; HSP70: heat shock protein; ANP: atrial natriuretic peptide; Cx43: mitochondrial connexin43.