Congenital left ventricular hypertrabeculation/noncompaction (LVHT) is a common feature of neuromuscular disorders (NMDs). Most commonly LVHT is located in the apex and the lateral wall. Acquired LVHT has been only occasionally reported. In myotonic dystrophy type 1 (MD1) acquired LVHT has not been described. In a 48-year-old female with MD1 due to a CTG-repeat expansion of 700–800 repeats in blood lymphocytes echocardiography at the age of 48 years revealed LVHT in the apex and the mid-ventricular septum. LVHT was interpreted as acquired since none of the previous echocardiograms, carried out to assess cardiac involvement in MD1, showed LVHT. Cardiac history and clinical cardiologic examination were normal. On ECG, non-specific ST-abnormalities and supraventricular ectopic beats were recorded. The AECG showed episodic sinus-bradycardia, ventricular ectopic beats, and was indicative of a sleep-apnea syndrome. This case is unique for the association of MD1 with acquired LVHT located in the apex and the mid-ventricular septum. In the absence of significant additional cardiac abnormalities no cardiac therapy was indicated.