Clinical presentation, occurrence of sudden infant death, and results of the available therapies in the largest group of patients with short QT syndrome (SQTS), studied so far, are reported. Clinical history, physical examination, electrocardiogram (ECG), exercise stress testing, electrophysiological study, morphological evaluation, genetic analysis and therapy results in 29 patients with SQTS and personal and/or familial history of cardiac arrest are reported. The median age at diagnosis was 30 years (range 4-80). In all subjects, structural heart disease was excluded. Eighteen patients were symptomatic (62%): 10 had cardiac arrest (34%) and in 8 (28%) this was the first clinical presentation. Cardiac arrest had occurred in the first months of life in two patients. Seven patients had syncope (24%); 9 (31%) had palpitations with atrial fibrillation documented even in young subjects. At ECG, patients exhibited a QT interval < or = 320 ms and QTc < or = 340 ms. Fourteen patients received an implantable cardioverter-defibrillator (ICD) and 10 hydroquinidine prophylaxis. At a median follow-up of 23 months (range 9-49), one patient received an appropriate shock from the ICD; no patient on hydroquinidine had sudden death or syncope. SQTS carries a high risk of sudden death and may be a cause of death in early infancy. ICD is the first choice therapy; hydroquinidine may be proposed in children and in the patients who refuse the implant.