This exon encodes 9–10 mainly acidic amino acids. It is normally included in embryonic avian and mammalian cardiac TnT (Jin et al., 1992) and abnormally expressed in adult canine hearts of dilated cardiomyopathy (Biesiadecki et al., 2002). Its inclusion equips myofibrils with a higher tolerance to acidosis and higher Ca2+ sensitivity. This evidence concerns the gene TNNT1 and dilated cardiomyopathy.