Background - Left ventricular dysfunction is a known predictor of ventricular arrhythmias. We hypothesized that measures of regional longitudinal deformation by speckle-tracking echocardiography predict ventricular tachyarrhythmias and provide incremental prognostic information over clinical and conventional echocardiographic characteristics. Methods and Results - We studied 1064 patients enrolled in the MADIT-CRT trial (Multicenter Automatic Defibrillator Implantation Trial-Cardiac Resynchronization Therapy) with speckle-tracking data available. Peak longitudinal strain was obtained for the septal, lateral, anterior, and inferior myocardial walls at baseline. The end point was the first event of ventricular tachycardia (VT) or fibrillation (VF). During the median follow-up of 2.9 years, 254 (24%) patients developed VT/VF. Patients with VT/VF had significantly lower left ventricular ejection fraction (28.3% versus 29.5%; P<0.001) and longitudinal strain in all myocardial walls compared with patients without VT/VF (anterior-strain, -7.7% versus -8.8%; P<0.001; lateral-strain, -7.3% versus -7.9%; P=0.022; inferior-strain, -8.3% versus -9.9%; P<0.001; septal-strain, -9.1% versus -10.0%; P<0.001). After multivariate adjustment, only anterior and inferior longitudinal strain remained independent predictors of VT/VF (anterior: hazard ratio, 1.08 [1.03-1.13]; P=0.001; inferior: hazard ratio, 1.08 [1.04-1.12]; P<0.001; per 1% absolute decrease for both). When including B-type natriuretic peptide in the model, only a decreasing myocardial function in the inferior myocardial wall predicted VT/VF (hazard ratio, 1.05 [1.00-1.11]; P=0.039). Only strain obtained from the inferior myocardial wall provided incremental prognostic information for VT/VF over clinical and echocardiographic parameters (C statistic 0.71 versus 0.69; P=0.005). Conclusions - Assessment of regional longitudinal myocardial deformation in the inferior region provided incremental prognostic information over clinical and echocardiographic risk factors in predicting ventricular tachyarrhythmias. Clinical Trial Registration - URL: http://www.clinicaltrials.gov. Unique identifier: NCT00180271.