Determination of the number of mRNA copies of KCNQ1 (LQTS1) and KCNH2 (LQTS2) was supposed to confirm the presence of the long-QT syndrome in the group of patients from the families in whom the syndrome has been previously diagnosed on the basis of supraventricular arrhythmia by ECG. The gene discussed is KCNQ1; the disease is Prolonged QT interval.