Isolated non-compaction of the ventricular myocardium (INCVM) is a relatively newly defined clinicopathologic entity. INCVM is clinically accompanied by depressed ventricular function, arrhythmias, and systemic embolization. We report two cases of INCVM with long QT syndrome (LQTS). In both cases the QT interval was over 0.55 s with episodes of torsades de pointes, and prominent ventricular trabeculations and deep intertrabecular recesses were detected by 2-dimensional echocardiography. Both cases had the KCNH2 mutation. To the best of our knowledge, this is the first report investigating INCVM with LQTS.