The long-term relationship between cardiac arrhythmias and sleep apnoea in myotonic dystrophy (DM1) is unknown. Pacemakers enabling the long-term monitoring of electrocardiographic and ventilation parameters were implanted in 20 patients with DM1 (mean age = 42+/-11.6 years), followed 40+/-12.3 months. Arrhythmias were recorded by the pacemaker in 17 patients (85%): 14 developed arrhythmic episodes that occurred either in absence or in presence of concomitant sleep apnoea. Conversely, among these 14 patients, the majority of sleep apnoea episodes were not associated with concomitant arrhythmias. In the other three patients who developed arrhythmias, simultaneous sleep apnoea was never observed. Episodes of sleep apnoea were observed in all patients, though only 85% presented with sleep apnoea syndrome. In conclusion, a high incidence of arrhythmias and sleep apnoea was observed. While arrhythmias are generally attributable to an organic substrate, they are sometimes precipitated by functional triggers, as in the case of sleep apnoea.