To prevent unexpected sudden cardiac patient death due to drug-induced Long QT syndrome (LQTS), we seek to build a computerized early detection and warning system of QTc interval increase tendency. We built an ECG database system that holds the digital waveform data and related information of the ECGs performed in out hospital, and developed an experimental detection system of QTc increase tendency. Despite the several problems about the accuracy of detection, we succeeded in extracting a patient who seemed to be drug-induced LQTS. A combination of such a detection system with more accuracy and drug prescription database would contribute to the early detection of drug-induced LQTS.