A 52-year-old man presented with sudden onset of palpitations and dizziness. Echocardiogram confirmed the diagnosis of isolated noncompaction of ventricular myocardium with moderated systolic dysfunction, and the electrocardiogram (ECG) revealed ventricular tachycardia (VT), of which the focus seemed to match an area of prominent left ventricular noncompaction on the 12-lead surface ECG. Through the activation mapping from the endo- and epicardium, simultaneously, a discrete potential preceding the QRS during VT was observed at the anterolateral epicardial wall. He subsequently underwent radiofrequency ablation, and VT was successfully eliminated.