A hereditary cardiac disease characterized by a prolongation of the QT interval at basal ECG and by a high risk of life-threatening arrhythmias. The disease is familial long QT syndrome (Monarch Disease Ontology id MONDO_0019171). Also known as: LQTS, Long QT Syndrome, Romano-Ward long QT syndrome, Romano-Ward syndrome, Ward-Romano syndrome, congenital long QT syndrome, hereditary long QT syndrome.