To answer whether the higher or lower TH availability in mice translated into altered expression of genes associated with hypo- or hyperthyroidism (13) and TH target gene expression of myosin heavy chain alpha (Myh6) and beta (Myh7), ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting 2 (Serca2a2) and ryanodine receptor 2 (Ryr2) was analyzed in mouse hearts, sacrificed after 2 and 4 weeks of treatment. This evidence concerns the gene RYR2 and hyperthyroidism.