a. Hybridization of dystrophin B isoform RT-PCR (oligonucleotides within B exons 1 and 6; expected product: 514 bp) with an internal oligo probe (within exon 2) that confirmed its expression in both Atria (lanes 2 and 4) and in the control brain (lane 6), and its absence in the Ventricles and Total Heart. b Levels of dystrophin M transcript expression (2-ΔΔCT values) using the skeletal muscle as internal calibrator and actin as reference gene in: Skeletal Muscle, Total heart, Right Atrium, Right Ventricle, Left Atrium, Left Ventricle, Sinoatrial (SA) Node, Atrioventricular (AV) Node, Bundle of His and Purkinje Fibres. The M isoform was expressed in all the samples studied, featuring the lowest score in Brain. c Levels of dystrophin B transcript expression (2-ΔΔCT values) using the brain as internal calibrator and actin as reference gene in the same samples. In both the ventricles the B amplification threshold cycle (CT) was undetermined, as well as in the total heart and in the conduction system structures. In the atria the score obtained was higher than that in skeletal muscle, in particular in the left atrium.