While trastuzumab has been shown to prevent recurrences of breast cancer, some women may also experience damage to their heart muscle (including heart failure) as a result of their treatment. The investigators hope to learn if standard medications used in heart failure can prevent heart damage caused by trastuzumab in women with breast cancer. The investigators would also like to know if there are any ways to detect this damage earlier using magnetic resonance imaging (MRI) and blood tests.

We propose a randomized, placebo-controlled, double-blind study evaluating the efficacy of an ACE-inhibitor (perindopril) or a beta blocker (bisoprolol) for the prevention of LV remodeling among women with early breast cancer scheduled for chemotherapy and one year of trastuzumab. Participants will undergo cardiac MRI at baseline and 3 and 12 months, replacing the usual MUGA, as well as a post-treatment cardiac MRI at 24 months to evaluate long-term effect.

Inclusion Criteria:

• Histologic diagnosis of HER2 positive breast carcinoma
• Eligible to receive trastuzumab
• Age > 18 years
• Able to give informed consent
• No contraindications to MRI

Exclusion Criteria:

• Known contraindication to beta-blocker therapy
• Known contraindication to ACEI therapy
• Current treatment with ACEI or beta blocker for other indication
• History of heart failure, cardiomyopathy or baseline LVEF < 50%