It has been reported that intracardiac electrogram T-wave alternans (IE-TWA) is greater prior to spontaneous ventricular tachyarrhythmia (VTA) than for baseline recordings.To investigate IE-TWA just prior to VTA episodes and at baseline and compare these with microvolt TWA (M-TWA) measured during exercise.We analyzed right ventricular ring-can electrogram recordings just prior to VTA episodes and compared T-wave pattern and degree of variation to baseline recordings from 3 patients (2 with idiopathic ventricular fibrillation and 1 with hypertrophic cardiomyopathy) who were enrolled in the Japan Intracardiac Electrogram TWA Study of ICD Recipients. In a stable state, we measured the M-TWA of the surface electrocardiogram during treadmill exercise in these 3 patients.We found 3 patterns of IE-TWA among these 3 patients with implantable cardioverter-defibrillator immediately prior to spontaneous VTAs. Case 1 had AB pattern of IE-TWA, case 2 ABC pattern, and case 3 nonspecific pattern but great T-wave amplitude variations. These IE-TWA amplitudes and the distribution of T-amplitude difference were greater than at baseline. Case 1 had a positive outcome in regard to the M-TWA determination, whereas cases 2 and 3 did not.We indicate different patterns of IE-TWA prior to spontaneous VTAs. The phenomena of IE-TWA correspond to outcomes of M-TWA measured during exercise in the surface electrocardiogram.