Isolated left ventricular noncompaction cardiomyopathy (IVNC) is a cardiomyopathy thought to be caused by arrest of normal embryogenesis of the endocardium and myocardium. This abnormality is often associated with other congenital cardiac defects. A 21-year-old man presented to the emergency department with worsening exertional dyspnea during the previous 2 months. Two-dimensional and Doppler echocardiography revealed an enlarged left atrium (LA) and a markedly dilated left ventricle (LV) with preserved LV systolic function, severe mitral valve regurgitation, and prolapse due to chordae rupture. The myocardium of the LV and right ventricle (RV) had excessively prominent trabeculations and deep intertrabecular recesses. He is the first patient in Korea who has undergone mitral valve replacement surgery because of severe mitral valve regurgitation and prolapse due to chordae rupture accompanied by IVNC.