Background: Cardiotoxicity associated with chemotherapeutic therapeutic agents such as tratsuzumab is a significant issue. Older age is one of the known risk factors of tratsuzumab-associated cardiotoxicity. We evaluated the left ventricular systolic function using 2D speckle tracking echocardiography in patients receiving tratsuzumab therapy. Methods: Breast cancer patients who were receiving tratsuzumab therapy were studied. Any patients who developed symptomatic congestive heart failure or decline of left ventricular ejection fraction (LV EF, %) more than 10% were excluded. Forty patients were enrolled and divided into the two groups according to age: group 1, ���50 years (n=25, 62.5%); group 2, <50 years (n=15, 37.5%). LV EF and global longitudinal peak strain (GLPS) before initiation of tratsuzumab therapy and during follow-up were determined using standard 2D and speckle tracking software. Results: Mean age was 52짹9 (32~69) years. Thirty-nine patients (97.5%) were female. Frequency of previous use of anthracycline or radiation therapy was comparable in the two groups (data not shown). All of the baseline (group 1, 59.5짹2.6% vs. group 2, 58.1짹2.6%, p=0.131), follow-up LV EF (group 1, 59.4짹3.1% vs. group 2, 58.3짹2.5%, p=0.280) and ��LV EF (group 1, 0.2짹4.4% vs. group 2, 0.2짹3.0%, p=0.295) were comparable between the two groups. Although baseline GLPS was similar in both groups (group 1, -20.4짹2.4% vs. group 2, -20.9짹2.7%, p=0.556), follow-up GLPS (group 1, -19.6짹2.2% vs. group 2, -21.7짹1.9%, p=0.004) ��GLPS (group 1, 0.8짹2.4% vs. group 2, -0.8짹2.2%, p=0.039) were significant decreased in the patients of group 1 than in those of group 2. Conclusions: Asymptomatic patients ���50 years receiving tratsuzumab therapy showed decline of GLPS without change of LV EF. GLPS can demonstrate subtle LV systolic dysfunction rather than LV EF.