We extracted L., the newborn of a diabetic mother, for antenatal diagnostic of myocardial hypertrophy and anomaly of foetal heart rate. Post-natal echocardiography showed severe septal myocardial hypertrophy with latero-basal myocardial akinesia. We did not observe a Doppler gradient through the left ventricular outflow. Selective coronary angiography showed an occlusion of the circumflex artery. Myocardial hypertrophy is a classic complication in newborns of diabetic mothers. The mother's diabetes and neonatal infarction remain an exceptional association. We discuss a different hypothesis to explain coronary occlusion and how myocardial infarction avoided septal obstruction.