BACKGROUND Although plasma brain natriuretic peptide (BNP) levels have been widely measured in patients with acute myocardial infarction (AMI), it is still uncertain whether the early recanalization modulates the levels and whether the levels can predict chronic stage left ventricular function. This study was designed to elucidate these issues. METHODS In 80 consecutive patients with AMI, plasma BNP levels were measured at admission and at 4 hours, 24 hours, 48 hours, and 1 month after admission. RESULTS In 35 of the 80 patients, the infarct-related artery was patent within 6 hours from the onset of MI (6-hour patency group), and in 27 patients, the artery was still occluded after 6 hours (6-hour occlusion group). The remaining 18 patients in whom it was unclear whether recanalization of the infarct-related artery had occurred within 6 hours or not were excluded from the analyses. In the 6-hour patency group, the BNP level gradually increased and reached a maximum value at 24 hours after admission. In the 6-hour occlusion group, the level increased more, with the values at 4 hours, 24 hours, and 48 hours significantly higher than those in the 6-hour patency group (86 +/- 18 pmol/L versus 35 +/- 8 pmol/L; P <.01; 112 +/- 13 pmol/L versus 74 +/- 9 pmol/L; P <.05; 102 +/- 15 pmol/L versus 53 +/- 11 pmol/L; P <.01). Chronic stage left ventricular function was correlated with not only the BNP level at same stage but also that at 24 hours and that at 48 hours after admission. Multiple regression analysis indicated that the BNP level at 24 hours was the most powerful predictor of chronic stage left ventricular function. CONCLUSIONS Plasma BNP levels can predict subsequent cardiac function. In addition, the importance of early recanalization may also be supported with BNP kinetics.