Myotonic dystrophy protein kinase is a multi-domain protein kinase found in muscle that is activated in response to G protein second messengers and proteolysis (1). DMPK is implicated in myotonic muscular dystrophy (DM), an autosomal dominant-inherited disorder that predominately affects skeletal and cardiac muscle and causes defects in cardiac conduction (2,3). DM arises through expansion of CTG repeats in the 3’-UTR of the DMPK gene (4). Mutant DMPK transcripts with an extended region of CUG repeats are retained in the nucleus (5). These transcripts also influence the expression of the DM locus-associated homeodomain protein (DMAHP)/SIX5, to mediate in part the DM phenotype (6). Other substrates for DMPK include myogenin, L-type calcium channels, and Phospholemman (PLM) (1).