Background:Clinical and experimental observations indicate that reduced beat‐to‐beat changes in the cycle length of nonsustained ventricular tachycardia (NSVT) may portend malignant ventricular tachyarrhythmias and sudden cardiac death. The purpose of the study was to test the hypothesis that measures of ventricular rate variability during NSVT (VRV‐NSVT) may be useful in identifying patients at high risk of life‐threatening arrhythmic events.Methods:The study group consisted of 326 patients who had NSVT on 24‐hour ECG recordings. Temporal changes in up to 10 beat‐to‐beat intervals of NSVT runs (V‐V) were assessed. The following parameters of VRV‐NSVT were calculated: (1) average value of successive differences in V‐V intervals (ADVV); and (2) normalized average value of successive differences in V‐V intervals (nADVV).Results:During a mean follow‐up of 4 years, 52 (16%) patients had a documented episode of sustained VT or ventricular fibrillation. Patients with these arrhythmic events had significantly (P<0.001) lower values of ADVV and nADVV variables in comparison to patients without arrhythmic events. The relative risk of malignant arrhythmic events for patients with ADW<40 ms was 4.9 (P<0.001), for patients with nADVV<6%, the risk was 3.9 (P<0.001).Conclusions:The results of this study indicate a strong and significant relationship between NSVT and the risk of subsequent malignant ventricular tachycardia. The assessment of VRV‐NSVT may be useful for identifying patients at high and low risk for sub