The association of markers of myocardial injury and dysfunction with infarct size (IS) and ejection fraction (EF) are well documented. However, limited data are available on the newer high-sensitivity troponin assays and comparison with morphologic and functional assessment with cardiac magnetic resonance imaging. We aimed to examine the associations of high-sensitivity cardiac Troponin-T (hs-cTnT), creatine kinase MB iso-enzyme (CKMB), and N-terminal pro B-type Natriuretic Peptide (NT-proBNP) to IS and EF at 6 months. Blood samples from 119 ST-segment elevation myocardial infarction patients from the Rapid Endovascular Catheter Core Cooling Combined With Cold Saline solution as an Adjunct to Percutaneous Coronary Intervention for the Treatment of Acute Myocardial Infarction trial were collected at baseline, 6, 24, and 48 hours after admission. Cardiac magnetic resonance was performed at 4 ± 2 days and 6 months. The association of biomarker levels to IS and EF was tested with Pearson's correlation coefficients and linear regression models with bootstrap resampling. The correlation coefficient of biomarker to IS was (CKMB: r = 0.71); (NT-proBNP: r = 0.55); (hs-cTnT: r = 0.80); and for EF (CKMB: r = 0.57); (NT-proBNP: r = 0.48); and (peak hs-cTnT: r = 0.68). IS and EF at 4 ± 2 days had the strongest correlations with IS and EF at 6 months respectively (IS: r = 0.84) and (EF: r = 0.74). Receiver operating characteristic of peak hs-cTnT for predicting EF ≤40% at 6 months was 0.87 compared with 0.75 for early IS. Early EF was a negative predictor of late EF <40%, 1-area under curve = 0.93. In conclusion, high-sensitivity Troponin T is a rapid, cheap, generally available tool for accurate prediction of systolic dysfunction in patients 6 months after first-time ST-segment elevation myocardial infarction.