To investigate the dynamics of plasma cAMP/cGMP in patients during cardiac surgery, and its relationship to traumatic stress. Methods: Sixteen patients, aged 19.31 years± 10.4 years , who underwent an open heart operation with cardiopulmonary bypass (CPB) and hy pother mia were served as subjects. The arterial plasma concentrations of cyclic adenos ine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were measured by radioimmunoassay 2 hours before operation, after heparinization, 20 minutes following CPB, at the end of the operation, and 24 and 72 hours postoperatively, respectiv ely. The patients preoperative blood samples were heparinized and the venous b lood samples of 30 healthy blood donors were taken to measure the levels of cAMP and cGMP as heparin and normal controls separately. Results: There were no statistical difference among the heparin control, preoperative level and normal control. The peak values of cAMP and cGM P occurred during CPB and plasma cAMP levels changed synchronously with intensit ies of operative stimulus to human body. However cGMP level was mainly related t o the operative stimulus to the heart and CPB. The cAMP value was positivel y correlated with the cGMP value (r= 0.6313 , P< 0.001 ).Conclusions: Dynamic variation of plasma cyclic ribonucleotide can be considered as a reference parameter for intensity of traumatic stress. To investigate the dynamics of plasma cAMP / cGMP in patients during cardiac surgery, and its relationship to traumatic stress. Methods: Sixteen patients, aged 19.31 years ± 10.4 years, who underwent an open heart operation with cardiopulmonary bypass (CPB) and hy pother mia were served as subjects. The arterial plasma concentrations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were measured by radioimmunoassay for 2 hours before operation, after heparinization, 20 minutes following CPB, at the end of the operation, and 24 and 72 hours postoperatively, respectiv ely. The patients’ preoperative blood samples were heparinized and the venous b lood samples of 30 healthy blood donors were taken to measure the levels of cAMP and cGMP as heparin and normal controls separately. Results: There were no statistical difference among the heparin control, preoperative level and normal control. The peak values ​​of cAMP and cGM P occurred during CP B and plasma cAMP levels changed synchronously with intensit ies of operative stimulus to human body. However, cGMP level was mainly related to the operative stimulus to the heart and CPB. The cAMP value was positivel y correlated with the cGMP value (r = 0.6313, P <0.001) .Conclusions: Dynamic variation of plasma cyclic ribonucleotide can be considered as a reference parameter for intensity of traumatic stress.