Short QT syndrome (SQTS) is a hereditary lethal arrhythmia; it was first described in 2000. SQTS is characterized by an abnormal short QT interval on electrocardiogram (ECG), and causes arrhythmia, such as ventricular fibrillation and atrial fibrillation. Although clinical characteristics of SQTS have not been appropriately elucidated, several victims, individuals in the teenage and those in their 20s, have been reported. Therefore, SQTS diagnosis at an early age is important and is recognized as a concern in a school screening program for heart disease. According to an expert consensus statement published in 2013, even an asymptomatic individual with a short QT interval, who has neither a family history nor a pathogenic gene mutation, can be diagnosed with SQTS. Studies with various adult populations have identified individuals who met the SQTS diagnostic criteria; however, these patients were asymptomatic and did not have a poor prognosis. Some asymptomatic children and adolescents with SQTS were also identified in our study, in which we mainly focused on a school screening program for heart disease. Risk stratification of SQTS is necessary because clinical characteristics of SQTS are variable, including no symptoms and sudden cardiac death. Hence, we compared the ECGs of asymptomatic individuals with a short QT interval in a school screening program for heart disease with those of previously reported symptomatic patients with SQTS, to screen for SQTS patients with a high risk. A prospective study thus needs to be conducted to elucidate the prognosis of asymptomatic patients with SQTS who are diagnosed in their childhood.