Steinerts disease or myotonic dystrophy type 1 is a genetic neuromuscular disorder with autosomal dominant transmission. It leads to multisystemic damage, including a cardiac localization that is life-threatening.We report the case of a 55 year old patient, without cardiovascular risk factors, with a history of distal muscle damage since the age of 25 years, in his family history we find a brother followed for an unlabelled skeletal muscle damage.He consulted for exertional dyspnea and lipothymic discomfort. The clinical examination revealed a decrease in muscle strength in the lower limbs with amyotrophy. Walking is difficult with the help of crutches and the patient uses a wheelchair. The neurological investigation concluded in Steinerts myotonic dystrophy on the electromyogram.The patients ECG showed a bifascicular block consisting of a left anterior hemiblock and a complete right bundle branch block. The echocardiography did not show any structural abnormalities but found a disturbance of the LV relaxation on the mitral profile.The electrophysiological exploration carried out for the measurement of infrahisical conduction revealed a long HV at 100ms indicating the implantation of a double chamber stimulation.The interest of reporting this case was to underline the importance of screening for cardiac damage of rhythmic origin. But also to inform with the help of literature data the incidence of these forms and the place of cardiac stimulation in the prevention of sudden death in steinerts myotonia.