Background: Whereas N-terminal pro-brain natriuretic peptide (NT-proBNP) is approved for risk stratification of patients with acute coronary syndromes (ACS), short-term temporal changes in NT-proBNP concentrations and the optimal time points for sampling are not clear. The purpose of this study was to better define the short-term changes in NT-proBNP in relation to clinical presentation, reperfusion and prognostic value in patients with ACS, as well as to identify the optimum time points for sampling. Methods: We studied daily plasma concentrations of NT-proBNP in 133 unselected patients with myocardial infarction (n=65), stable coronary artery disease (CAD, n=46) and no CAD (n=22) who underwent coronary angiography. Results: Patients with non-ST-elevation myocardial infarction (NSTEMI) presented with markedly higher NT-proBNP than patients with ST-elevation myocardial infarction (STEMI) [1305 (741–3208) ng/L vs. 170 (70–424) ng/L, p<0.001]. Also, time to presentation from onset of pain was much longer in NSTEMI as compared to STEMI (>48 h vs. <6 h, p<0.001). Patients with NSTEMI also presented with higher NT-proBNP as compared with CAD [224 (98–732) ng/L] and no CAD [47 (26–102) ng/L; p<0.001, NSTEMI vs. both]. Following successful percutaneous coronary intervention [thrombolysis in myocardial infarction (TIMI) 3-flow established], NT-proBNP increased markedly within 24 h in patients with STEMI [718 (379–1338) ng/L, p<0.01 vs. 0 h], whereas no change in NT-proBNP was noted in patients with NSTEMI [1190 (1010–2024) ng/L, p=0.88 vs. 0 h]. In both STEMI and NSTEMI, NT-proBNP decreased significantly 96 h after successful reperfusion [STEMI –52%, 372 (189–610) ng/L, p<0.05; NSTEMI –52%, 613 (365–724) ng/L, p<0.05]. Unsuccessful reperfusion (TIMI<3) was associated with unchanged or increased NT-proBNP. NT-proBNP at 96 h and peak NT-proBNP further displayed a strong correlation with cardiac troponin T (r=0.64 and r=0.54, p<0.001), a marker of infarct size, and NT-proBNP at 96 h was a strong predictor of long-term prognosis (hazard ratio 7.29, p=0.025). Conclusions: In patients with NSTEMI, NT-proBNP may be increased as high as concentrations usually associated with acute congestive heart failure despite the absence of clinical signs. In contrast, patients with STEMI and short time to presentation may present with completely normal NT-proBNP, but dramatic short-term increases following reperfusion. NT-proBNP reflects ischemic burden, reperfusion success and prognosis, and the current data support repetitive sampling in patients with ACS. Clin Chem Lab Med 2010;48:875–81.