BACKGROUND:Left ventricular hypertrabeculation (LVHT) has not been described in myotonic dystrophy Type I (MD1) before. CASE REPORT:A 42-year-old man developed typical features of MD1 since 1992. Creatinekinase was slightly, but recurrently elevated. Needle electromyograms were myogenic and showed extensive spontaneous activity. Muscle biopsy was compatible with MDI. DNA analysis revealed a heterozygous 300 CTG-repeat expansion in the myotonic-dystrophy proteinkinase gene on chromosome 19q13.3. Cardiac history and clinical cardiologic examination were normal. On ECG, ST elevation and atrial flutter were found. The AECG was normal except for atrial flutter. Surprisingly, transthoracic echocardiography revealed LVHT, previously described only in Becker's muscular dystrophy, mitochondriopathies, and Barth syndrome. CONCLUSION:A rare cardiac manifestation of MD1 may be LVHT which alone has no therapeutic implication.