Noncompaction cardiomyopathy (NCC) is a rare congenital disease of heart muscle that affects both children and adults. It results from abnormal prenatal development of heart muscle.

During development, the majority of the heart muscle is a sponge-like meshwork of interwoven myocardial fibers. As normal development progresses, these trabeculated structures undergo significant compaction that transforms them from spongy to solid. This process is particularly apparent in the ventricles, and particularly so in the left ventricle. Noncompaction cardiomyopathy results when there is failure of this process of compaction. Because the consequence of non-compaction is particularly evident in the left ventricle, the condition is also called left ventricular noncompaction. Other hypotheses and models have been proposed, none of which is as widely accepted as the noncompaction model.

Symptoms range greatly in severity. Most are a result of a poor pumping performance by the heart. The disease can be associated with other problems with the heart and the body.

Subjects' symptoms from non-compaction cardiomyopathy range widely. It is possible to be diagnosed with the condition, yet not to have any of the symptoms associated with heart disease. Likewise it is possible to have severe congestive heart failure, even though the condition is present from birth, which may only manifest itself later in life. Differences in symptoms between adults and children are also prevalent with adults more likely to have heart failure and children from depression of systolic function.

Common symptoms associated with a reduced pumping performance of the heart include:

Two conditions though that are more prevalent in noncompaction cardiomyopathy are: tachyarrhythmia which can lead to sudden cardiac death and clotting of the blood in the heart.^{[citation needed]}

The presence of NCC can also lead to other complications around the heart and elsewhere in the body. These are not necessarily common complications and no paper has yet commented on how frequently these complications occur with NCC as well.^{[citation needed]}

The American Heart Association's 2006 classification of cardiomyopathies considers noncompaction cardiomyopathy a genetic cardiomyopathy. Mutations in LDB3 (also known as "Cypher/ZASP") have been described in patients with the condition. There is recent information in which NCC has been seen in combination with 1q21.1 deletion Syndrome. Furthermore, mutations in DES (desmin), TTN (titin), RBM20 and LMNA could be detected in a large cohort of LVNC patients. Loss-of-function variants in the NONO gene have been associated with an X-linked form of noncompaction cardiomyopathy in males who also often present with developmental delays. TPM1 has also been implicated in development of the disease.