The appearance of serum troponin T (tn-T) on day 1 after acute myocardial infarction (AMI) strongly depends on coronary reperfusion. In contrast, the kinetics of tn-T release after day 1 after AMI are unaffected by the reperfusion status, and reflect the degradation of myofilaments in irreversibly damaged cells. However, it is not known whether serum tn-T levels after day 1 after AMI can be used to predict the long-term outcome. The purpose of this study was to elucidate the prognostic value of determining the tn-T level on day 3 or 4 after AMI. Serum tn-T levels on day 3 or 4 after AMI were measured in 121 patients (92 men and 29 women, mean age 65 years). Mean follow-up period was 526 days. There were 12 deaths (9 cardiac and 3 noncardiac) during the follow-up period. By Kaplan-Meier analysis, patients with tn-T levels higher than the median level (6.9 ng/ml) had a significantly higher mortality rate than those with submedian levels (p <0.01). By multivariate Cox proportional-hazards regression analysis, the serum tn-T level was an independent predictor of the long-term outcome after AMI (p <0.01). Futhermore, in patients with a first AMI, the serum tn-T level exhibited a significant negative linear correlation with left ventricular ejection fraction assessed 4 weeks after AMI (r = -0.48, p <0.001). Increased serum tn-T levels on day 3 or 4 after AMI are a powerful noninvasive predictor of poor long-term prognosis, reflecting residual left ventricular function after AMI.