Mercy is leading the way with heart-sparing left breast radiotherapy using techniques to move the heart out of the radiation fields. The standard radiation may lead to an increased risk for cardiac disease. But with the deep-inspiration breath hold technique, patients breathe through a mouthpiece connected to an Active Breathing Coordinator (ABC) unit, which monitors lung volume. The operator closes a valve to produce a breath hold. A deep breath creates increased separation between the chest wall and heart by moving the breast outward and the heart and diaphragm downward. Radiation is delivered during these repeated breath holds.