In rodents, a single bout of exercise prior to injection of a chemotherapy agent used to treat breast cancer prevents or attenuates a number of markers of cardiac injury. This study will investigate whether this finding translates to human breast cancer patients. Participants scheduled to receive chemotherapy for breast cancer will be randomized to exercise or no exercise 24 hours prior to every chemotherapy treatment. The effect on cardiac function will be compared between groups noninvasively by echocardiography and electrocardiography and a venous blood draw at baseline before chemotherapy, after the first treatment and at the end of chemotherapy.