Breast cancer is the most common cancer amongst Canadian women. 15-20% of early breast cancers have high levels of a protein called HER2 which is associated with worse survival. Treatment of these patients with anthracyclines followed by trastuzumab (which targets HER2) improves survival. Unfortunately, these medications together can cause heart muscle injury resulting in heart dysfunction or failure in about 14% and 3.6% of the patients, respectively. Once heart failure (HF) occurs, about 60% of patients will not live past 2 years. Studies have suggested that patients with heart injury caused by anthracyclines may be more likely to develop HF with addition of trastuzumab. Therefore tests to find early heart injury after anthracyclines may allow doctors to start heart protective medications with the hope of preventing HF. Also, animal and small patient studies have shown that an increase in the water levels of the heart muscle (edema) may be an early sign of heart injury from anthracyclines. Cardiac MRI is a unique technique that has been shown to detect edema in various heart diseases.

The investigators will test the theory that, in women receiving treatment for breast cancer, heart edema detected by MRI at the end of anthracyclines will identify patients who will later develop heart dysfunction. MRI studies with novel techniques will be done pre-therapy, after anthracyclines, during herceptin, and at end of all therapy. The investigators will compare patients with and without heart dysfunction to test if patients with heart dysfunction are more likely to have edema after anthracyclines. Ultimately the investigators hope to use cardiac MRI to identify high risk patients and study various heart protective medications to prevent HF. This will improve the personal health of cancer patients by allowing them to live free of heart disease after their cancer therapy. Ultimately at a population level this will allow doctors to provide care that can be uniquely designed for each patient based on their individual risk.

The first 136 patients enrolled are included in the first part of the study, named EMBRACE-MRI 1. Enrollment for this part of the study is complete.

The remaining 44 patients will be enrolled into EMBRACE-MRI 2, which includes slight differences in obtaining sequences in MRI imaging.

Inclusion Criteria:

• Scheduled to undergo treatment with one of the following regimens: (a) 5-fluorouracil, epirubicin, cyclophosphamide, followed by docetaxel and trastuzumab, (b) adriamycin, cyclophosphamide, followed by docetaxel and trastuzumab, (c) adriamycin-cyclophosphamide with weekly paclitaxel and trastuzumab, or (d) dose dense adriamycin and cyclophosphamide followed by dose dense paclitaxel and trastuzumab
• Able to tolerate five ~60 minute CMR examinations over 15 months
• Able to give informed consent

Exclusion Criteria:

• Life expectancy < 12 months
• Participating in a clinical trial of a new cancer drug
• Having received previous anthracycline
• History of myocardial infarction or previous heart failure
• Current unstable angina, persistent atrial fibrillation or other irregular rhythm, or a history of more than mild regurgitant or stenotic valvular heart disease
• Severely reduced renal function (GFR ≤ 30 milliliters/minute)
• General MRI contraindications
• Baseline LVEF <55% by echo
• echocardiography image quality inadequate for strain analysis

Women ≥18 years with stage I-III, HER2+ breast cancer