Non-compaction of the left ventricular myocardium (LVNC) has gained increasing 
recognition during the last 25 years. There is a morphological trait of the 
myocardial structure with a spectrum from normal variants to the pathological 
phenotype of LVNC, which reflects the embryogenic structure of the human heart 
due to an arrest in the compaction process during the first trimester. It must 
be cautioned not to overdiagnose LVNC: the morphological spectrum of 
trabeculations, from normal variants to pathological trabeculations with the 
morphological feature of LVNC must be carefully considered. The classical triad 
of complications are heart failure, arrhythmias, including sudden cardiac death, 
and systemic embolic events. Non-compaction of the left ventricular myocardium 
can occur in isolation or in association with congenital heart defects (CHDs), 
genetic syndromes, and neuromuscular disorders among others. The clinical 
spectrum is wide and the outcome is more favourable than in previously described 
populations with a negative selection bias. Familial occurrence is frequent with 
autosomal dominant and X-linked transmissions. Different mutations in sarcomere 
protein genes were identified and there seems to be a shared molecular aetiology 
of different cardiomyopathic phenotypes, including LVNC, hypertrophic and 
dilated cardiomyopathies. Thus, genetic heterogeneity, with an overlap of 
different phenotypes, and the variability of hereditary patterns, raise the 
questions whether there is a morphological trait from dilated/hypertrophic 
cardiomyopathy to LVNC and what are the triggers and modifiers to develop either 
dilated, hypertrophic cardiomyopathy, or LVNC in patients with the same 
mutation. The variety in clinical presentation, the genetic heterogeneity, and 
the phenotype of the first transgenetic animal model of an LVNC-associated 
mutation question the hypothesis that LVNC be a distinct cardiomyopathy: it 
seems to be rather a distinct phenotype or phenotypic, morphological expression 
of different underlying diseases than a distinct cardiomyopathy.