To determine the relation between electromechanical endocardial mapping (EEM) and cardiac magnetic resonance (CMR) derived functional and viability parameters in patients with a large myocardial infarction. Forty-two patients with a large ST-elevation myocardial infarction underwent both EEM and CMR four months after primary percutaneous coronary intervention. EEM was performed to assess linear local shortening (LLS), unipolar voltage (UV) and bipolar voltage (BV). CMR cine imaging was performed to determine left ventricular global volumes, ejection fraction and regional function. Late gadolinium enhancement was used to assess size and transmural extent of infarction. Average LLS, UV and BV differed significantly between normal and dysfunctional segments (9.8 vs. 7.3, 11.8 vs. 9.7 and 3.3 vs. 2.8 for LLS, UV and BV respectively; p<0.001 for LLS and UV, p=0.006 for BV). In addition, average LLS, UV and BV, differed significantly between non-, subendocardial and transmural enhanced segments (10.8 vs. 8.8 vs. 5.0, 12.3 vs. 10.5 vs. 9.5 and 3.5 vs. 3.0 vs. 2.3 for LLS, UV and BV, respectively, p<0.001 for all variables). Although regional EEM data showed reasonable correlation with CMR, specific cut-off values for EEM parameters could not be established. EEM may be helpful in determining both the regional function and the transmural extent of infarction in patients with a large myocardial infarction. However, correlation with CMR parameters was moderate and exact cut-off values for EEM parameters could not be established. Further development of this potentially very useful modality is needed before it can be advocated for exact border-zone endocardial injection.