Clinical trials have demonstrated a small, yet significant risk of cardiac toxicity associated with radiation therapy for breast cancer. While radiotherapy plays a crucial role in treating breast cancer, it can cause incidental damage to the heart and lungs, that may in turn increase the risk of heart disease and lung cancer. Potential damage to the heart is influenced by the area of the chest where the tumour is located i.e. radiation targeted to the left breast increases the risk of damage to the heart. There has been some evidence that damage to the heart can be reduced by applying a particular radiation therapy technique (such as CT based radiotherapy planning) and the breath-holding technique. The breath-holding technique is where the lungs are expanded (upon inspiration) and the heart is pushed away, out of the path of the radiation. Cancer Council recommends you discuss questions and concerns about radiation treatment and its possible impacts on the heart with your radiation oncologist. You may want to ask the radiation oncologist about the dose of radiation you will be receiving and how the heart will be protected from the effects of radiation treatment.