Objective:To test the hypothesis that ventilator-associated pneumonia(VAP) after cardiac surgery with cardiopulmonary bypass(CPB) requires TLR4-dependent signaling. Methods:Twenty patients were categorized into two groups based on development of VAP following CPB,group with VAP (group A) and group VAP without (group B). The blood samples of left atrium were collected in both groups at the time points of preoperation(T1),20 min(T2),40 min(T3) and end(T4) of CPB. Expression of TLR4 on granular leukocyte was detected with flow cytometry. The cinical data of all cases in two groups were compared. Results:VAP occurred in 8 patients. CPB time in group A was statistically longer than in group B. The expression of TLR4 on granular leukocyte in group A at the time points of T3 and T4 were significantly higher than those in group B. Conclusion:Development of VAP after cardiac surgery with CPB was promoted by long CPB time via TLR4-dependent signaling activated.