The vertebrate splicing factor RBM20 (RNA binding motif protein 20) regulates protein isoforms important for heart development and function, with mutations in the gene linked to cardiomyopathy. Previous studies have identified the four nucleotide RNA motif UCUU as a common element in pre-mRNA targeted by RBM20. In humans, RBM20 contributes to the pathogenesis of a rare, progressive terminal cardiomyopathy ARVC characterized by fibrofatty replacement of cardiac muscle.