Objective:Left ventricular (LV) dysfunction after trastuzumab treatment in erb-2 breast cancer cases has been fully investigated. However, there is not enough data about the effect of trastuzumab treatment on right ventricular (RV) functions. This study is designed to evaluate the right heart changes by performing echocardiography after trastuzumab treatment in patients with erb-2 breast cancer.Methods:Forty-two consecutive breast cancer patients with erb-2 overexpression mean age 50.4±11.6 years who were decided to receive trastuzumab treatment were enrolled. Echocardiographic examinations including 2-D, spectral, and tissue Doppler measurements were performed at the baseline (T1) and repeated after 6 months (T2).Results:Tricuspid annular plane systolic excursion (TAPSE) was decreased, RV myocardial performance index (RVMPI) and tricuspid E/e’ ratio was increased after trastuzumab treatment (1.84 vs. 2.14; p<0.01) (0.46 vs. 0.56, p<0.01) (4.4±1.07 vs. 5.08±1.46; p=0.04). Median serum NT-ProBNP levels, troponin I, and hs-CRP levels were similar between the groups. LVEF and TAPSE were negatively correlated with dosage of trastuzumab (r=-0.392, p=0.04; r=-0.522, p=0.006). There was a stepwise decrease in LVEF when trastuzumab used with anthracyclines however this not reached statically significant (62.4±2, 60±4.5; p=0.06).Conclusion:In our study; we observed a trend of RV deterioration after trastuzumab treatment. These preliminary RV changes were demonstrated by using TAPSE, RV tissue Doppler imaging derived MPI and E/e’ ratio parameters by echocardiography and these parameters could also use as markers of trastuzumab toxicity in this population.