Background- Color tissue Doppler imaging M-mode through the mitral leaflet is an easy and precise method to estimate all cardiac time intervals from 1 cardiac cycle and thereby obtain the myocardial performance index (MPI). However, the prognostic value of the cardiac time intervals and the MPI assessed by color tissue Doppler imaging M-mode through the mitral leaflet in patients with ST-segment-elevation myocardial infarction (MI) is unknown. Methods and Results- In total, 391 patients were admitted with an ST-segment-elevation MI, treated with primary percutaneous coronary intervention, and examined by echocardiography a median of 2 days after the ST-segment-elevation MI. Outcome was assessed according to death (n=33), hospitalization with heart failure (n=53), or new MI (n=25). Follow-up time was a median of 25 months. The population was stratified according to tertiles of the MPI. The risk of new MI, being admitted with congestive heart failure or death, increased with increasing tertile of MPI, being ≈3 times as high for the third tertile compared with the first tertile (hazard ratio, 2.8; 95% confidence interval, 1.7-4.7; P