OBJECTIVE： To explore the effects of morphine combined with hyperbaric oxygen preconditioning on the related indicators in patients after heart value replacement in cardiopulmonary bypass. METHODS： 129 patients with heart value replacement in cardiopulmonary bypass were randomly divided into normal group （43 cases）， single group （43 cases） and combined group （43 cases）. Normal group intramuscularly injected atropine and phenobarbital 30 min before surgery， then conducted heart value replacement in cardiopulmonary bypass. Single group slowly injected Morphine hydrochloride injection 0.2 mg/kg when taking heart value replacement in cardiopulmonary bypass. On the basis of single group， combined group was additionally given medical hyperbaric oxygen chamber， once a day in the 3 day before surgery， and anesthesia induction was performed with midazolam， fentanyl and captopril in all groups. The heart， systolic blood pressure， diastolic blood pressure， pulse pressure， LVEF， cardiac function indexes（LAD， IVST， LVDD， PWT， LVM， LVMI）， T lymphocyte subsets （CD3+，CD4+，CD8+，CD4+/CD8+，Th1，Th2，Th1/Th2，Treg/CD4+，Th17/CD4+），IgA，IgM，IgG，complement C3，C4 levels before and after treatment， and the incidence of adverse reactions in all groups were observed. RESULTS： After surgery， LVEF in combined group was significantly higher than before， normal group and single group， LVDD and IVST were significantly lower than before， normal group and single group （P＜0.05）； CD8+，Th1， Th2， Th1/Th2， Th17/CD4+， complement C3 levels in single group and combined group were significantly lower than before and normal group， and combined group was lower than single group， CD4+，CD4+/CD8+，Treg/CD4+ were significantly higher than before and normal group， and combined group was higher than single group（P＜0.05）. There were no obvious adverse  reactions during treatment. CONCLUSIONS： Morphine combined with hyperbaric oxygen preconditioning can improve the cardiac functions and T lymphocyte subset levels in patients after heart value replacement in cardiopulmonary bypass， reduce complement C3 content， with good safety.