Left ventricular noncompaction of the myocardium is a rare genetic cardiac disease characterized by a prominent meshwork and deep intertrabecular recesses of the left ventricle. The condition has frequently been misdiagnosed as other cardiomyopathies. Sudden deaths due to the disease are rarely reported in the literature of forensic sciences. We report 2 cases of sudden death due to undiagnosed left ventricular noncompaction. One was a 30-year-old man who suddenly collapsed while eating breakfast. He was pronounced dead on arrival at the hospital. The other 24-year-old man had a witness collapse at home. Despite immediate resuscitation, he expired 11 hours after hospitalization. Postmortem examination revealed that both patients died of left ventricular noncompaction. The key pathologic findings are described. Additionally, the literature is reviewed, and the incidence, clinical and pathophysiologic presentation, pathogenesis, and diagnostic criteria for the left ventricular noncompaction are discussed.