Background: Breast cancer accounts for 10% of US female cancer cases and second in worldwide cancer fatalities. Overexpression of the ERBB2 oncogene in 20-25% of invasive breast tumors implies aggression. Trastuzumab improves outcomes via HER2. HER2-targeted chemotherapy with albumin-paclitaxel and Trastuzumab is used increasing survivability but may induce cardiotoxicity by blocking HER2. It works with chemotherapy for HER-2/neu positive breast cancer. Objectives: To evaluate Cardiac toxicity of concurrent Trustuzumab and Paclitaxel in Adjuvant treatment of HER-2 positive Breast Cancer Patients and methods: This was prospective hospital-based study at Qena University Hospital, with 30 participants post-radical surgery and anthracycline-based chemotherapy for unilateral ductal carcinoma, HER2-positive. Physical exams, lab tests, ECG, and Echo was done. Adjuvant trastuzumab administered with paclitaxel for 4 cycles, then continued for 1 year. Results: Age >55 (50%), obesity (43.3%), hypertension, hyperlipidemia (30%), diabetes (16.7%). Electrocardiogram (ECG) abnormalities increased after 4 cycles (16.7%), 6 months (23.3%), 9 months (33.3%), and 12 months with trastuzumab monotherapy (53.3%). ECG abnormalities were more common in trastuzumab monotherapy (46.7%) than in Paclitaxel (16.7%). P-wave, ST-segment, T-wave, and QRS changes were notable. Trastuzumab treatment increased T-wave alterations (20% vs. 0% baseline) and arrhythmias (33.3% vs. 3.3% baseline) after 12 months, but Paclitaxel did not (16.7% vs. 3.3% after 4 cycles). There was statistically significant decline in LVEF%, MAPSE, TAPSE, E/E and RV FAC and significant increase in LVESD, LVEDD, LVISD, LA, E/A after treatment by trastuzumab alone. Conclusion: LVEF% was significantly higher after 12 months of trastuzumab alone however, more patients developed ECG abnormalities.