The primary objective of this study was to determine the pattern of N-Terminal pro brain natriuretic peptide (NT-pro BNP) secretion pre and post cardiac surgery and then to investigate the correlation between levels of serum NT-pro BNP and postoperative clinical and biochemical endpoints. This was a prospective observational study performed at a tertiary centre in New Zealand, examining 118 adult patients undergoing cardiac surgery. Interventions included blood samples for NT-pro BNP and troponin-T taken 48 hours prior to operation and 12, 36 and 72 hours postoperatively. The plasma NT-pro BNP levels increased fourfold postoperatively, to plateau at 36 to 72 hours. Preoperative NT-pro BNP levels correlated with ventilation time (r = 0.46), length of stay in intensive care unit (r = 0.59), total perioperative noradrenaline dose (r = 0.55), but not with postoperative atrial fibrillation or mortality. Using multivariate analysis, serum NT-pro BNP levels at 36 hours were associated with increased noradrenaline dose (P = 0.001), decreased preoperative ejection fraction (EF) Group (P = 0.013) and elevated preoperative NT-pro BNP (P < 0.001). Factors not associated with NT-pro BNP levels at 36 hours include the operation type, bypass and cross-clamp times, use of milrinone and troponin-T We conclude that NT-pro BNP levels increased markedly after cardiac surgery and that high preoperative NT-pro BNP levels are associated with a slow postoperative recovery, but do not predict the occurrence of postoperative atrial fibrillation or mortality. Myocardial ischaemia is an unlikely cause of the NT-pro BNP elevation, because no correlation existed between troponin-T and NT-pro BNP levels.