OBJECTIVES: This study was designed to compare electroanatomic mapping (EAM) and magnetic resonance imaging (MRI) with delayed contrast enhancement (DCE) data for delineation of post-infarct scars. BACKGROUND: Electroanatomic substrate mapping is an important step in the post-infarct ventricular tachycardia (VT) ablation strategy, but this technique has not yet been compared with a gold-standard noninvasive tool informing on the topography and transmural extent of myocardial scars in humans. METHODS: Ten patients (9 men, age 71 +/- 10 years) admitted for post-infarct VT ablation underwent both a left ventricle DCE MRI and a sinus-rhythm 3-dimensional (3D) (CARTO) EAM (Biosense Webster, Johnson & Johnson, Diamond Bar, California). A 3D color-coded MRI-reconstructed left ventricular endocardial shell was generated to display scar data (intramural location and transmural extent). A matching process allocated any CARTO point to its corresponding position on the MRI map. Electrogram (EGM) characteristics were then evaluated in relation to scar data. RESULTS: A spiky EGM morphology, a reduced unipolar or bipolar EGM voltage amplitude (<6.52 and <1.54 mV, respectively), as well as a longer bipolar EGM duration (>56 ms) independently correlated with the presence of scar whatever its intramural position. Endocardial scars had a larger degree of signal reduction than intramural or epicardial scars. None of the parameters was correlated with transmural scar depth. A clear mismatch in infarct surface between CARTO and MRI maps was observed in one-third of infarct zones. CONCLUSIONS: Sinus-rhythm EAM helps identify the limits of post-infarct scars. However, the accuracy of EAM for precise scar delineation is limited. This limit might be circumvented using anatomical information provided by 3D MRI data.