PURPOSE To evaluate the correlation between scar as depicted by delayed enhancement (DE) MRI and the electrophysiological arrhythmogenic substrate in scar-related ventricular tachycardia (VT). METHOD AND MATERIALS 10 patients (4 ICM, 3 myocarditis, 2 ARVC, 1 non-ischemic DCM) underwent DE MRI at high spatial resolution (voxel size 0.625x0.625x2.5mm) prior to VT ablation. The endocardium and epicardium were manually segmented. Scar was automatically segmented on myocardial histogram with a threshold set at 3SD above mean signal of remote myocardium. From the segmented images, a digital 3D model was computed and imported in 3D mapping systems. During the mapping/ablation procedure, this model was co-registered in real time to the electrophysiological mapping geometry. Endocardial and epicardial contact mapping was performed at high density (>500 sites per map) during sinus rhythm (SR) and VT. The electrophysiological VT substrate (abnormal/late activity during SR, critical isthmus during VT) was correlated to DE MRI data. RESULTS The integration of MRI data enabled a 3D visualization of the endocardium, epicardium and scar during the mapping/ablation procedure. VT was mapped in 7/10 patients. Critical isthmuses located within scar areas in 4 patients (2 myocarditis, 1 ICM, 1 ARVC), and at the border zone (<6mm from scar) in 3 patients (3 ICM). Epicardial isthmuses matched sub-epicardial scar at MRI in all cases (3/3, 2 myocarditis, 1 ARVC). SR was mapped in all patients. The target for ablation in SR (abnormal/late activity) matched myocardial scar at DE MRI in all patients (10/10). CONCLUSION The electrophysiological VT substrate correlates to DE at MRI. The integration of DE MRI data in 3D mapping systems is useful to guide mapping/ablation of scar-related VT. CLINICAL RELEVANCE/APPLICATION The integration of DE MRI data in 3D mapping systems is useful to guide mapping/ablation of scar-related VT