Hypoplastic left heart syndrome in the second trimester.

Hypoplastic left heart syndrome is a relatively common congenital anomaly with a high mortality even after palliative postnatal surgery. The case presented had a normal cardiac cavity and great artery dimensions at 19 weeks of gestation but bright left ventricular myocardial echoes, impaired left ventricular shortening, and no detectable forward flow in the left ventricular outflow tract. Autopsy showed left ventricular subendocardial calcification. This demonstrates a likely early stage in the evolution of hypoplastic left heart syndrome, which has a variable time course. The abnormal left ventricular myocardial performance associated with low left ventricular output results in a failure of growth of the left heart rather than there being a primary failure of embryogenesis.