The chemotherapy medications used for breast cancer treatment are important for achieving a cure, but a potential side effect is that they can cause a decline in functional capacity (reduced exercise tolerance and impaired physical function) and increase the risk of cardiovascular disease. The risks of decreased functional capacity and cardiovascular disease are highest in breast cancer survivors as they grow older. The factors causing the decline in functional capacity are not well understood, however they may be related to a reduction in cardiac function (e.g. decreased pumping ability of the heart) or skeletal muscle function (reduced muscle blood flow and oxygenation). Exercise training is used for other populations at risk for cardiovascular disease (such as cardiac rehabilitation), but is not routinely offered to breast cancer survivors. Therefore this research study wants to test whether exercise training can improve heart and muscle health, and increase functional capacity in up to 60 older breast cancer survivors aged \>60 years old who previously received chemotherapy drugs that can affect the heart. The purpose of this study is to compare two rehabilitation approaches: a 12-week structured exercise training program or a 12-week stretching-yoga program. The investigators want to compare whether these programs can improve functional capacity, and heart and skeletal muscle function. To do this, some of the participants in this study will be randomly enrolled in the structured exercise training program and others will be randomly enrolled in the stretching-yoga program.