hypoplastic left heart syndrome

Hypoplastic left heart syndrome is a severe defect in which the entire left side of the heart, the chamber and valves that normally pump blood to the body, is critically underdeveloped. Hypoplastic means underformed. It is as though the heart's main engine was built far too small to drive the body's circulation.

Because the left ventricle cannot do its job, the newborn survives only as long as fetal shortcuts remain open: blood must cross the foramen ovale and the right ventricle must pump to the body through the ductus arteriosus. When that duct naturally closes in the first days of life, the body's blood supply collapses, making this one of the most urgent newborn cardiac emergencies.

There is no simple fix. Management involves keeping the ductus open with medication, then a staged series of operations over the first years that rebuild the circulation so the single working right ventricle pumps to the body, or, in some cases, heart transplantation. Outcomes have improved greatly but the condition remains serious and demands lifelong specialist care.