Background:The clinical value of T-wave variability (T-var) for ventricular arrhythmia (VA) risk prediction was evaluated.Methods and Results:Three 20-min Holter-ECG-based T-var measurements (I1 at baseline, I2 after 6.5±1.6 months and I3 after 13.1±2.0 months) were done in 121 patients. T-var was defined as the amplitude variability of the T-wave with the maximum of T-wave oscillation. The endpoint was a fast, potentially fatal VA (>240 beats/min). During follow-up (20±4 months) 20/121 patients (55% ischemic heart disease, 15% preserved left ventricular ejection fraction [LVEF]) had fast VA terminated by ICD or external shock. Although T-var did not differ between patients with vs. without fast VA at baseline (I1: 10.7±7.3 µV vs. 7.8±4.1 µV, P=0.170), patients with fast VA had higher T-var compared to those without fast VA at 2 subsequent measurements (I2: 14.0±6.5 µV vs. 8.2±3.6 µV, P=0.030; I3: 17.0±5.4 µV vs. 8.8±4.6 µV, P=0.004). The increase in T-var between I1 and I2 was higher in patients with fast VA (∆T-var=7.0±9.3 µV), as compared to patients without (∆T-var=0.4±4.3 µV). After adjustment for LVEF in a multiple logistic regression model, the odds ratio for developing fast VA was 1.1 (P=0.056) for each 1-µV increment in T-var at I1.Conclusions:T-var is elevated in patients with fast VA, and both elevation of T-var and increase in T-var may complement LVEF in VA risk stratification. (Circ J 2015; 79: 318–324)