We evaluated the ability of electromechanical mapping (EMM) to discriminate between normal, viable, and nonviable (scarred) myocardium in patients with coronary artery disease versus dobutamine stress echocardiography (DSE) when the correspondence between the test and reference data sets is established via a common 3-dimensional reconstruction of the left ventricle. We studied 21 patients with coronary artery disease who underwent angiography, biplane ventriculography, and EMM within 1 month of DSE. A 3-dimensional left ventricular (LV) reconstruction was prepared from the ventriculogram and spatially aligned with EMM. EMM measurements of unipolar voltage, bipolar voltage, and local linear shortening were projected onto the three-dimensional left ventricle, averaged in each of 16 segments, and compared with DSE viability (normal, viable, scar) assessed at a core laboratory. All of the EMM measurements varied significantly (p <0.001) between the normal, viable, and scarred myocardium as assessed by DSE. Local linear shortening for normal, viable, and scarred segments was 10.4 ± 6.5%, 7.8 ± 5.6%, and 4.8 ± 4.4%, respectively. In discriminating between these 3 groups, local linear shortening was more powerful than unipolar voltage or bipolar voltage (F = 20.765, F = 10.655, F = 4.795, respectively). Local linear shortening correlated best with viability, perhaps because it shares the same cognitive function as DSE. Three-dimensional analysis provides an anatomic framework that enables direct comparison of data from multiple imaging modalities rather than assuming segmental correspondence. Our results show that EMM provides significant on-line, diagnostic information on myocardial viability assessed by DSE on a segment-by-segment basis.