Myotonic dystrophy type 1 (MD) is the most common autosomal dominant muscular dystrophy in adults. Cardiac involvement is mainly characterized by conduction abnormalities and arrhythmias. We sought to assess diastolic function in MD patients. Echocardiography-Doppler was performed in Steinert's patients and in a control group completed by tissue Doppler imaging (TDI). Twenty-six patients with Steinert's disease were included in the study and were compared to a control group. Mean age was similar in the 2 groups (45.1 years ±10.9 in Steinert's patients vs 42.1 years ±11 in control group p 0.4). 6 /26 patients with Steinert's disease disclosed a left ventricular (LV) ejection fraction <50%. Mean left atrial (LA) diameter was statistically different between Steinert's patients and patients in group control (27.8 mm ±8.5 vs 19.7 mm ±4; P=0.0018). Mean peak E/A mitral ratio was 1.29±0.45 in Steinert's patients vs 1.36±0.4 in control group (P=0.6). We found an increase of the mitral E deceleration time in Steinert's patients in comparison with patients in control group (219 ms ±53 vs 176 ms ±29; P=0.013). Mean peak lateral early diastolic velocity Ea was similar in the 2 groups (12.3 cm/s ±3 vs 13.1 cm/s ±3.8; P=0.50). Mean peak septal early diastolic velocity was similar in the 2 groups (11.2 cm/s ±2 vs 10.4±2; P=0.51). We found an increase of the LA diameter and an increase of the mitral deceleration time in Steinert's patients that suggest diastolic abnormalities.