Abstract: Objective To investigate the relationship between the variation of LVEF(left ventricular ejection fraction) and cardiotoxicity in Innermongulia breast cancer patients who received chemotherapy regimen combined trastuzumab. Methods Follow up the breast cancer patients′ LVEF at the interval 3 months from the first beginning of trastuzumab to the 12 months after the last dose of trastuzumab since October 2008 to December 2011. Results The LVEF level decreased 5.5% when finished trastuzumab treatment in both adjuvant chemotherapy group or salvage chemotherapy group. The LVEF level in 3 of the patients decreased more than 10% while had no any heart failure symptoms. Two patient developed palpitations after 12 months of trastuzumab treatment while had normal LVEF level. Conclusion From the results of LVEF change for the patients accepted trastuzumab treatment combined adjuvant chemotherapy or salvage chemotherapy, the treatment is safe to the patients. LVEF is a suitable parameter to evaluate the safety of the treatment method, while it′s value in predicting early cardiotoxicity is limited.