A heart-lung machine is a medical device used during certain types of surgery, especially heart surgery. It takes over the functions of the heart and lungs by pumping blood and adding oxygen to it. This allows surgeons to operate on a still and bloodless heart, making complex procedures safer and more effective. When the heart is stopped, the heart-lung machine ensures that oxygen-rich blood continues to flow to the rest of the body. It is a crucial tool in modern medicine, enabling life-saving surgeries and improving outcomes for patients with heart conditions.