A 8-year-old white female was referred to our attention for a suspected Long QT syndrome. The clinical history was negative for cardiac events. The prolongation of the QTc was initially observed after assumption oi Qf proiongi.rg drugs (clarithromycin). However, even without those drugs and with normal potassium values, the QTc wai still prolonged (QTc 490 ms in D2) and during the recovery phase of exercise a iurther prolongation of the QT, associated with the appearance of notched T waves in V2-V3, was observed. Echocardiography showed normal features. LQTS genes were screened through DHPLC and sequence analysis. A double mutation was identified, one on KCNQ1 (A372D), already described as a disease-causing mutation and a second novel one (R1175C) in the intra-cellular loop between D2 and D3 on SCNSA. This second mutation is in a highly conserved aminoacid and was not identified in 150 controls'