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BACKGROUND Sudden nocturnal death is a syndrome that usually affects patients with diabetes mellitus type 1 (DM1), being described mainly due to ventricular arrhythmias in response to nocturnal hypoglycemia. OBJECTIVES Evaluate the relation between hypoglycemia and ventricular arrhythmias in patients with DM1 and normal structural heart. METHOD Prospective, observational study with DM1 patients and normal structural heart on echocardiogram aged 18-60 years, of both sexes receiving insulin therapy for at least five years. Intermittent glucose reading device was implanted (iPro2 - Medtronic / USA) and 24hr ambulatory electrocardiographic recording by the Holter system (Cardios Systems - Brazil). Patients were monitored for hypoglycemia without any type of induction (interstitial glucose <70mg/dl) and cardiac arrhythmias within 24 hours. RESULTS Thirty-two patients were evaluated, with mean-age of 35 years, being 16 men. Eleven patients (34%) did not have hypoglycemia, other 3 (27.3%) also had no arrhythmia, while 8 (72.7%) had arrhythmias interpreted as irrelevant. The other 21 patients (66%) presented some hypoglycemic episodes and 10 (47.6%) did not present arrhythmias, whereas 11 (52.4%) presented arrhythmias considered not clinically significant, as also found in non-diabetic individuals. CONCLUSION In patients with DM1 without structural heart disease there was no relationship between cardiac arrhythmia and episodes of hypoglycemia.