The difference between the arterial and the end-tidal carbon dioxide tension [P(a-E1)CO2] was observed before and after cardiopulmonary bypass(CPB)was performed in 34 patients,who were divided into 3 groups according to the duration of CPB.It was found that there was an increase of P(a-E1)CO2 after CPB in all the patients and the increase was more significant in Group C(CPB duration of 158 to 186 minutes)than in Group A(CPB duration of 82 to 106 minutes)(P