In mirror image experiments we have shown that Mbnl1−/− loss results in arrhythmias, cardiac histopathology and sudden death and Lee et al. have further demonstrated that Mbnl1−/−/Mbnl2+/− mice show both arrhythmias, left ventricular hypertrophy with myocardial fibrosis25, 52. Here, MBNL1 is linked to cardiac arrhythmia.