Inclusion Criteria:

• ≥18 years of age,
• New diagnosis of HER2+ breast cancer,
• Planned adjuvant (post-surgery) HER2-directed therapy,
• And meeting either criteria #2 or #3 below for cardiac dysfunction risk. The latter is defined in the 2017 clinical practice guidelines on the prevention and monitoring of cardiac dysfunction in cancer patients by American Society of Clinical Oncology (ASCO).41 Three groups of cancer patients are deemed to be at risk of cardiac dysfunction and HF:
  1. Any patient receiving high-dose anthracycline (e.g., doxorubicin ≥ 250 mg/m2), high-dose radiotherapy (RT ≥ 30 Gy) where the heart is in the treatment field, or lower-dose anthracycline in combination with lower-dose RT, where the heart is in the treatment field,
  2. Treatment with lower-dose anthracycline or trastuzumab alone with any of the following risk factors:
     • ≥2 cardiovascular risk factors, including smoking, hypertension, diabetes, dyslipidemia, and obesity, age ≥60 years, compromised cardiac function (e.g. history of myocardial infarction, ≥ moderate valvular heart disease),
  3. Treatment with lower-dose anthracycline followed by trastuzumab (sequential therapy).

Exclusion Criteria:

• History of HF of any class and type, or diagnosis of cardiomyopathy in the past,
• LVEF <53% at screening,
• Baseline use of cardvedilol, nebivolol or bisoprolol,
• Current ACE inhibitor or ABR therapy for hypertension in the presence of diabetes and/or for chronic kidney disease/proteinuria,
• Intolerance to beta-blocker,
• Current anti-arrhythmic drug therapy,
• History of bronchial asthma or related bronchospastic conditions,
• Heart rate < 50 BPM at screening,
• History of or current sick sinus syndrome,
• AV block grade II or higher (unless patient has a permanent pacemaker) at screening,
• Systolic blood pressure < 90 mmHg at screening,
• Severe hepatic dysfunction, as defined by NCI ODWG (total bilirubin >3x ULN, any AST elevation) or Child Pugh C class
• Pregnancy,
• Inability to provide informed consent.