BackgroundDepolarization　abnormalities　are　hardly　detectable　by　standard　12-lead　electrocardiogram　(ECG)　in　some　patients.　ObjectiveTo　evaluate　the　value　of　the　16-lead　High-Definition　(HD)-ECG　machine　to　record　conduction　abnormalities　including　Epsilon　waves　in　patients　with　structural　heart　disease.　MethodsTracings　with　12-lead　ECG,　16-lead　HD-ECG,　and　signal-averaged　ECG　were　studied.　Results(1)　Case　of　severe　coronary　artery　disease　(CAD):　On　16-lead　HD-ECG,　a　tiny　intra-QRS　signal　was　noted　in　lead　III,　a　prolonged　P　wave　in　lead　II,　and　fragmentation　on　top　of　lead　aVL　and　lead　aVF.　Proper　automatic　measurement　of　the　prolonged　P　wave　measuring　190ms　was　noted.　Signal-averaging　by　16-lead　HD-ECG　in　lead　III　showed　the　intra-QRS　fragmentation　and　P　wave　prolongation　of　180ms.　(2)　First　patient　with　arrhythmogenic　right　ventricular　dysplasia　(ARVD):　Standard　12-lead　ECG　indicated　Epsilon　waves　in　lead　III,　V2,　V3,　and　inverted　T　waves　in　V1-V3.　16-lead　HD-ECG　indicated　QRS　prolongation　in　lead　II,　III,　aVL,　aVF,　V2,　V3　as　opposed　to　V6,　and　low　amplitudes　of　QRS　complexes　in　V4R　and　V3R　as　a　new　possible　sign　of　ARVD.　Notches　in　lead　V2,　widening　of　QRS　complexes　in　all　precordial　leads,　but　shorter　QRS　in　V8-V9　are　also　considered　as　a　potential　new　diagnostic　sign　of　ARVD.　(3)　Second　ARVD　patient:　Notches　at　the　end　of　the　QRS　in　lead　III　and　a　negative　initial　deflection　of　the　QRS　in　V1　and　V2　were　detected　by　standard　12-lead　ECG.　On　16-lead　HD-ECG,　a　more　pronounced　QRS　fragmentation　was　visible.　Conclusion16-lead　HD-ECG　in　both　CAD　and　ARVD　seems　to　be　more　sensitive　than　12-lead　ECG　to　record　electrocardiographic　abnormalities.