We describe an occurrence of long QT syndrome in association with persistent patency of the arterial duct in members of a family. Patency of the arterial duct was diagnosed in family members of 4 successive generations. The index case had long QT syndrome associated with such a patent duct. Another patient had long QT syndrome, but associated with a ventricular septal defect. We postulate that there may be a common genetic mechanism for long QT syndrome and persistent patency of the arterial duct.