(See also Overview of Arrhythmogenic Cardiomyopathies and Overview of Arrhythmias) Non-compaction cardiomyopathy is a rare (1 in 7000) cardiomyopathy resulting from failure of the embryonic ventricular myocardial compaction process, such that the ventricular myocardium consists of an outer layer of normally compact myocardium and an inner non-compacted layer that has retained embryonal characteristics.