Breast cancer can be managed using chemotherapy, endocrine therapy and biological therapy. Treatment is determined and specified according to the characteristics of the tumor including overexpression of the human epidermal growth factor receptor (HER2). Previously patients who were diagnosed with HER2 positive breast cancer were considered of poor survival but after the discovery of trastuzumab, disease free survival among these patients was improved significantly. Though trastuzumab has made great improvement in the treatment of breast cancer, it was identified to possess a major side effect which is cardiotoxicity . Cardiotoxicity that occurs with anticancer agents is usually manifested as left ventricular dysfunction (LVD) and overt heart failure (HF). LVD was defined as a decrease in cardiac LV ejection fraction (LVEF), that is either global or more severe in the septum, symptoms of congestive heart failure (CHF), associated signs of CHF including but not limited to S3 gallop, tachycardia or both and decline in LVEF of at least 5% to below 55% with accompanying signs or symptoms of CHF, or a decline in LVEF of at least 10% to below 55% without accompanying signs or symptoms. Beta blockers have shown a cardioprotective effect against chemotherapy induced- cardiotoxicity. Nebivolol is a third-generation beta blocker. It is highly selective to B1- adrenergic receptors. It also has peripheral vasodilating effect due to its effect on L-arginine/ nitric oxide pathway in the endothelium of blood vessels. The dose of nebivolol given in the study was 5mg/day for the entire period of the study. Echo was done for all patients to determine the changes of left ventricular ejection fraction in patients in the treatment group and control group. The study concluded that nebivolol prevented the occurrence of anthracycline induced cardiotoxicity. the current study will be the first clinical trial to evaluate the cardioprotective effect of nebivolol on trastuzumab-induced cardiotoxicity in breast cancer patients. Aim of the work Evaluation of the effect of Nebivolol on trastuzumab - induced cardiotoxicity in non-metastatic breast cancer patients by assessment of: * Left ventricular ejection fraction. * Cardiac biomarkers (troponin- Pro- BNP). * Treatment safety. * Patient quality of life (Using fact-B questionnaire)