Radiotherapy (RT) to the breast or chest wall of young women is associated with long-term cardiotoxicity and an increased risk of secondary breast cancers. As many patients with early stage breast cancer and Hodgkin's disease are cured of their disease, there is significant concern regarding the long term risks of therapy. Older RT techniques for treating the breast/chest wall and draining lymph nodes for breast cancer resulted in a relatively high dose being delivered to a substantial volume of heart, and convincing evidence exists of excess cardiovascular morbidity and mortality in patients treated with these techniques. While modern RT techniques have reduced radiation exposure to the heart, they have not eliminated it. Many large studies of Hodgkin's disease survivors have demonstrated a clear risk of secondary breast cancer development after mantle RT for Hodgkin's disease. The risk of developing breast cancer after mantle RT appears to be related to age at time of irradiation, dose delivered to the breast tissue, and whether or not chemotherapy is incorporated into the overall treatment plan. In this article we review late cardiac complications associated with tangential breast RT and the risk of developing a secondary breast cancer after mantle RT for Hodgkin's disease.