Cardiac surgery usually leads to postoperative immunosuppression, which is characterized by predisposition to develop secondary nosocomial infections and high risk of tumorigenesis and development. Current studies showed that acupuncture treatment was effective on immunoregulation. Our previous study proved that electroacupuncture (EA) can regulate the innate immune system overreaction to endotoxin and reduce excessive inflammatory response induced by myocardial ischemia and reperfusion. However, whether transcutaneous electrical acupoint stimulation(TEAS) can improve immune function in patients post cardiac surgery is not clear. The investigators perform a randomized controlled study to evaluate whether TEAS treatment can improve the immunosuppression post cardiac surgery, which may provide rational for the development of TEAS to treat cardiac patients perioperatively.