Although cardiac complications are well known in myotonic dystrophy (DM), patients rarely manifest symptoms of cardiac disease, and if so they most often show conduction abnormalities or arrhythmia. In this study, specific cardiac findings were reviewed in 79 patients with DM. No correlation was found between the cardiac assessments and the CTG expansion. Thus, for a single patient the cardiac involvement in the disease can not be predicted from the findings of the genetic investigation. On the other hand, a clear positive relationship of the PR interval with the QRS duration was revealed, as well as a positive correlation between the age of the DM patient and the QRS duration, which increases with 0,54 ms/year. Systolic dysfunction, evaluated by transthoracic echocardiography, seems to be quite uncommon. In 32 % of the patients with a normal ECG, the 24 h Holter monitoring showed arrhythmias and conduction abnormalities. Based on these findings we recommend a follow up of DM patients not only based on the ECG, but also through 24 h Holter monitoring.