To develop a heart-dysfunction model of DM1 in flies, we have generated UAS-CTG transgenic lines carrying 20 [CUG(20)×] or 250 [CUG(250)×] pure CTG repeats and crossed them with the cardiac-specific driver GMH5-Gal4 (Wessells et al., 2004), which includes the UAS-GFP reporter, allowing the labeling of the tissues in which Gal4 is expressed. Here, LGALS4 is linked to myotonic dystrophy type 1.