Background: Several markers of systemic inflammation seem to play an active role in the pathophysiology of acute coronary syndrome and its evolution. High mobility group box-1 (HMGB-1), a ubiquitous nuclear protein constitutively expressed in quiescent cells, was recently recognized as a newer critical mediator of inflammatory diseases. The present study aimed to evaluate the possible association between HMGB-1 levels and structural and functional indices of cardiovascular performance such as cardiopulmonary and Doppler-echocardiography indices in patients after acute myocardial infarction (MI). Methods and Results: Fifty-four consecutive patients (mean age 58.3 years, 83% males) recovering from acute MI were included in the study protocol. All patients underwent Doppler-echocardiography, cardiopulmonary exercise, and HMGB-1 assay. HMGB-1 levels in acute MI patients were significantly higher compared with age- and body mass index-matched controls (14.8 +/- 6.8 vs. 2.3 +/- 1.0 ng/mL, P < .0001, respectively). Postinfarction patients showed oxygen consumption at peak exercise (VO2peak) = 14.4 +/- 4.2 mL.kg.min and a slope of increase in ventilation over carbon dioxide output (VE/VCO2slope) = 32.1 +/- 6.2, whereas Doppler-echocardiography values were: left ventricular end-diastolic volume (LVEDV) = 53.4 +/- 8.2 mL/m(2); left ventricular ejection fraction (LVEF) = 41.7 +/- 7.0%. Multiple linear regression analysis (stepwise method) showed that VO2peak (beta = -0.276, P = .012), VE/VCO2slope (beta = 0.244, P = .005), LVEDV (beta = 0.267, P = .018), peak creatine kmase-MB (beta = 0.339, P = .004), peak Troponin I (beta = 0.244, P = .002), and LVEF (beta = -0.312, P = .021) were significantly associated with HMGB-1 levels. Conclusions: The present study demonstrated that in postinfarction patients, HMGB-1 levels were significantly higher compared with controls, and significantly correlated with cardiopulmonary and Doppler-echocardiography parameters. (J Cardiac Fail 2009;15:362-367)