AbstractWe report on two prenatal ultrasound diagnoses of left ventricular non‐compaction cardiomyopathy (LVNC) associated with mutation of the cardiac β‐myosin heavy chain gene (MYH7). LVNC is characterized by a trabecular meshwork and deep intertrabecular myocardial recesses communicating with the left ventricular cavity. Clinical features range from non‐penetrant disease in adult carriers to heart failure, arrhythmia and thromboembolism. Both cases showed cardiomegaly on prenatal ultrasound examinations, with features indicating non‐compaction of the myocardium apparent in the third trimester. Mutations in the MYH7 gene were identified postnatally in each case in both the proband and the father. One infant underwent surgical mitral valvuloplasty and a mechanical valve implant later; in the other, left ventricular function was unimpaired at birth. Cardiac function in both cases remained stable at last follow‐up. These cases highlight the importance of prenatal ultrasound diagnosis of LVNC and the need for cardiologic and molecular testing of first‐degree relatives who may be unknown carriers of an MYH7 mutation.