PURPOSE Previous studies demonstrated that secretion of circulatory effective peptides was stimulated in cardiac surgery associated with ECC. Human adrenomedullin(AM), one of circulatory effective peptides, is synthesized in endothelial cell and vascular smooth muscle cell(VSMC). Secreted mature AM(MAM), maturated by intracellular amidation, associates with its specific receptor on VSMC and acts as a vasorelaxant. We hypothesized that AM secretion would be affected by ECC because of its crucial role in regulation of peripheral vascular tone, especially in the reduction of cardiac after-load after cardiac surgery. Therefore, we investigated the influence of cardiac surgery with ECC on AM secretion and its correlations with hemodynamic parameters in this study. PATIENTS AND METHODS Plasma samples for measurement of AM were collected in nine patients with cardiac surgery(CABG in seven, CABG and AVR in one, and AVR and MVR in one) at following time points: pre-operation, 3 minutes after initiation of ECC, 10 and 60 minutes after cross clamp of aorta, 10 minutes after declamp of aorta, 10, 60 minutes, 6 hours after weaning from ECC, and 1,3,5, and 7 days after operation. Plasma total AM and mature AM were measured by immuno-radio metric assay. Heart rate(HR), arterial blood pressure(ABP), central venous pressure(CVP), pulmonary artery pressure(PAP), pulmonary capillary wedge pressure (PCWP), and cardiac output were monitored as hemodynamic profiles. RESULTS Total AM(TAM) and MAM concentration at pre-operation were 11.9±4.8 fmol/ml and 1.1±0.2 fmol/ml, respectively. The concentration of TAM and MAM at 10 minutes, 60 minute, 6 hours and 24 hours after weaning from ECC, increased significantly compared with ones at pre-operation, and during ECC. Amidation ratio of AM, the ratio MAM to TAM, at 10 and 60 minutes after weaning from ECC were decreased significantly compared with ones during ECC. The decrease ratio in calculated SVRI at 10 minutes after weaning from ECC to the ones at pre-operation significantly correlated with the increase ratio in plasma TAM at 60 minutes after weaning from ECC to the ones at pre-operation. CONCLUSION In cardiac surgery, plasma TAM and MAM were altered after discontinuation of ECC. Significant decrease of AM amidation ratio indicated that this AM alternation was attributed to the stimulation of the AM production rather than the stimulation of the AM maturation. Furthermore, significant correlation between SVRI and TAM suggested that the stimulation of the endogenous AM production might be attributed to hemodynamic changes induced by ECC.