Abstract： Aim To investigate the predictive value of serum miR-21 and miR-30b in the cardiac toxicity of trastuzumab tar-geted therapy after breast cancer surgery.Methods 138 patients with breast cancer who were treated with trastuzumab were se-lected as the observation group,and were divided into two subgroups:non-cardiotoxic group and cardiotoxic group according to whether there were chemotherapy-related cardiac toxicity events.In addition,150 healthy women who underwent physical examinations during the same period were selected as the healthy group.The levels of serum miR-21 and miR-30b and clinical data in each group were compared.ROC was used to evaluate the predictive value of serum miR-21 and miR-30b for the occurrence of cardiac toxicity,and multiple Logistic regression analysis was used to identify the influencing factors of cardiac toxicity.Results The serum miR-21 in the observation group were higher than that in the healthy group,while miR-30b was lower than that in the healthy group.The serum miR-21 and hypertension proportion in the cardiotoxic group were higher than that in the non-cardiotoxic group,while miR-30b and left ventricular ejection fraction(LVEF)were lower than that in the non-cardiotoxic group(P＜0.05).LVEF,miR-21 and miR-30b were the influencing factors of cardiac toxicity of chemotherapy after breast cancer surgery(P＜0.05).The diagnostic efficacy of ser-um miR-21 and miR-30b in predicting the cardiac toxicity of chemotherapy after breast cancer surgery was higher than that of miR-21 and miR-30b alone(P＜0.05).Conclusion Serum miR-21 and miR-30b are the influencing factors of cardiac toxicity of chemo-therapy after breast cancer surgery,and the combination of them is more effective in predicting the cardiac toxicity of chemotherapy af-ter breast cancer surgery.