INTRODUCTION: Myotonic dystrophy is a multisystem disease associated with cardiac abnormalities that are responsible for high morbidity and mortality. It commonly affects conduction tissue, resulting in changes in heart rate that tend to progress with age. OBJECTIVE: The aim of the study was to assess overall cardiovascular risk and the risk of arrhythmias in patients with myotonic dystrophy type 1 (DM-1) and to correlate them with genetic study (CTG expansion size). METHODS: This retrospective study included 31 DM-1 patients referred to the cardiology department of Centro Hospitalar Entre Douro e Vouga by the neurology department for screening for heart disease. Patients\' medical records were consulted for the diagnostic tests performed in the diagnostic cardiology consultation: electrocardiogram (ECG), high-resolution ECG, heart rate variability (HRV), Holter 24-hour ambulatory ECG and transthoracic echocardiogram (TTE); results of genetic testing were also consulted. RESULTS: Of 31 patients studied, 38% had first-degree atrioventricular block (AVB) and 51% had intraventricular conduction disturbances (62% had late potentials). TTE revealed no structural heart disease. Rare supraventricular and ventricular ectopic beats were the most common arrhythmias on 24-hour Holter monitoring. The sample showed lower HRV, reflecting vagal dysfunction. Patients with larger CTG expansions had more cardiac abnormalities. CONCLUSIONS: Patients with DM-1 had arrhythmic events, with AVB and more significantly intraventricular block, although none had malignant arrhythmias or structural heart disease. No patient died. Patients with larger CTG expansions had greater involvement of cardiac conduction tissue.