Background: Although adenosine (ADO) has been shown to have beneficial effects against tissue injury after myocardial ischaemia, the controversy still remains regarding the optimal timing, dose, temperature, method of ADO administration and duration of exposure to the drug. This study investigates the cardioprotective effect of exogenous ADO pretreatment as an adjunct to 1 mmol l-1 ADO cold (12 °C) blood cardioplegia during heart valve replacement surgery. Materials and methods: Thirty patients with rheumatic heart valve disease undergoing heart valve replacement operations were randomly assigned to two groups: group C (n = 15) and group A (n = 15). Patients in group C were the control group and received antegrade cold (12 °C) high-potassium ([K⁺] = 20 mol l^-1) institute blood cardioplegia. The patients in group A received 10-min 100 μg kg^-1 min^-1 ADO pretreatment before application of the aortic cross-clamp and antegrade 1 mmol l^-1 adenosine high-potassium ([K⁺] = 20 mol l^-1) cold (12 °C) blood cardioplegia. Clinical outcomes were observed before, during and after the operation. Plasma level markers of myocardial damage: cardiac Troponin I (cTnI), creatine kinase (CK-MB) and inflammatory factors (interleukin (IL)-6 and IL-8) were obtained from serial venous blood samples after induction, 5 min after cross-clamp of aorta, 10 min after clamp-off, 1 h after return to ICU and postoperatively 24 h and 48 h. Right atrial samples were harvested before cross-clamp and after clamp-off. Results: Heart valve replacement was successful in all patients. There were no differences regarding operative parameters in the two groups. Time to arrest (during cardiolegia perfusion electrocardiography (ECG) change to a line) was shorter in group A compared to group C (19.9 ± 4.6 s vs 29.3 ± 10.6 s; p = 0.03). Group A also had lower cTnI and IL-8 levels (p = 0.03) at 10 min after aortic declamping, and lower IL-6 (p = 0.04) at 24 h postoperatively as well. Ultrastructural changes were slighter in group A than group C after clamp-off. Compared to group C, post-reperfusion biopsies in group A displayed only slight overall ultrastructural changes, and scored significantly better on mitochondrial damage (group A 2.23 ± 0.65 vs group C 2.85 ± 0.66) (p = 0.04). Conclusion: Compared with simple cold blood cardioplegia in heart valve replacement patients, ADO pretreatment as an adjunct to 1 mmol l^-1 ADO cold blood cardioplegia may reduce cTnI, IL-6 and IL-8 release, resulting in reduced myocardial injury in ultrastructure after surgery. © 2009 European Association for Cardio-Thoracic Surgery.