<p>  Left ventricular non-compaction cardiomyopathy (LVNC) is a disease in which the compaction leading to the formation of the normal myocardial structure during the embryonic period is impaired. LVNC is characterized by a left ventricle with marked trabecular meshwork. The disease can cause heart failure similar to dilated cardiomyopathy, embolism as a result of mural thrombosis, or electrocardiographic abnormalities including a fatal arrhythmia. We report a child with LVNC who exhibited a pronounced QTc prolongation during general anesthesia.</p><p>  An eight-year-old boy who was found to have an abnormal electrocardiogram two years earlier and had been diagnosed as having LVNC was scheduled to undergo general anesthesia for the extraction of a mesiodens. His preoperative electrocardiogram showed QTc prolongation (529 ms) with flat or inverted T waves at all leads.</p><p>  On the day of surgery, monitoring including electrocardiography, non-invasive blood pressure (NIBP) monitoring, pulse oximetry, and muscle relaxant monitoring were performed. During anesthesia, the QTc and estimated continuous cardiac output (esCCO ; Nihon Kohden, Tokyo, Japan) were also measured. The patient was anesthetized using remifentanil, thiamylal and rocuronium and anesthesia was maintained using with air, O₂, sevoflurane and remifentanil. QTc prolongation (600-650 ms) was observed after the administration of thiamylal and also during awakening. No arrhythmia, such as premature ventricular contraction, and no fluctuations in NIBP, heart rate, or esCCO were observed. His postoperative course was uneventful.</p><p>  During anesthesia for children with LVNC and QT prolongation, intraoperative circulatory fluctuations must be monitored, and careful attention must be given to the possible occurrence of arrhythmias. The continuous monitoring of intraoperative QTc and esCCO might be useful.</p>