Breast cancer patients are treated with a combination of different drugs that unfortunately can harm their heart and in some cases can cause heart failure. To limit the damage from these drugs on the heart, it is important for the doctors to know how well the heart is working before, during and after treatment. Imaging the heart (e.g. using Magnetic Resonance Imaging (MRI)) can tell us how well the heart is pumping blood to the rest of the body. If the heart has been harmed then it is likely that less blood will be pumped out of the heart. We would like to test another MRI technique called phosphorous spectroscopy. This has the potential to tell us how well the cells of the heart are working and could give us an earlier warning that the patients heart is at risk of damage. Their cancer treatment could then be changed before further damage is done to their heart.