Isolated non compaction of the left ventricle is a rare congenital cardiomyopathy linked to an arrest of normal myocardial embryogenesis. We report two cases of isolated non compaction of the left ventricle discovered by echocardiography in 2 males of 30 and 55 years. The first had progressively worsening cardiac insufficiency, the second was being followed for an unexplained cardiomyopathy. In both cases, the diagnosis was able to be confirmed by transthoracic echocardiography, supported by MRI data. Although present from birth, this condition can become apparent at various ages and is complicated by sudden death (principal cause of mortality), severe cardiac insufficiency, or thrombo-embolic accidents. The diagnosis of left ventricular non compaction should be considered when faced with unexplained cardiac insufficiency in the adult.