Objective To investigate the effect of cold autologous blood cardioplegia and HTK solution on changes of superoxide dismutase (SOD) and Matrix metalloproteinase-2 (MMP-2) in infant coronary sinus vein blood,which underwent ventricular septal defect suture in extracorporeal circulation,in order to reveal their protective effect of autologous cold blood cardioplegia on immature myocardium.Methods Sixty cases with ventricular septal defect,aged less 1-year-old,were randomly divided into experimental group (n =30) and control group(n =30).Autologous cold blood cardioplegia was obtained on aortic blood before aortic root draw in extracorporeal circulation with K + concentration of 20 mmol/L and 4 ℃ temperature.The experimental group was used cold autologous blood cardioplegia as arresting and protecting cardioplegia,while the control group used HTK solution.Blood sample from coronary sinus and vein was obtained at immediately before aortic cross-clamping,1 minute and 15 minutes after aortic cross-opening.SOD and MMP-2 levels were determined by enzyme-Linked Immuno Sorbent Assay (ELISA).Results The levels of SOD and MMP-2 levels within the group,between the groups and interaction were significant difference (P ＜ 0.05).After aortic cross-opening,the level of SOD and MMP-2 of the experimental group and the control group were increased (P ＜ 0.05).Before aortic cross-clamping,The activity of SOD in experiment was(85.37 ± 16.82) mU/L,as same as that in the control group((91.51 ± 15.02) mU/L,P ＞ 0.05).The MMP-2 concentration was in experiment group was (362.29 ±29.52) μg/L,as same as that in the control group((372.32 ± 31.42) μg/L,P ＞ 0.05).At 1 minute after aortic cross-opening,there were significant differences regarding of SOD and MMP-2 levels between the both groups(SOD ∶ (106.97 ± 17.46) mU/L vs.(98.74 12.54) mU/L,P ＜ 0.05 ; MMP-2 ∶ (439.48 ± 51.62) μg/L vs.(465.49 ±48.83) μg/L,P ＜0.05) ;The same trend was seen at 15 minutes after aortic cross-opening in two groups in terms of SOD and MMP-2 level (SOD:(104.03 ± 12.63) mU/L vs.(97.94 10.87) mU/L,P ＜0.05; MMP-2:(390.16 ±45.63) μg/L vs.(425.21 ±48.24) μg/L,P ＜0.05).Compare to group B,arrhythmia incidence(x2 =8.223,P ＜ 0.05) and positive inotropic drug dependent degree was lower in group A (x2 =4.022,P ＜ 0.05).Conclusion The cold autologous blood cardioplegia could promote the release of SOD in immature myocardium and reduce the production of MMP-2,which has endogenous protective effect for the infant Imature myocardium.