Heart-lung machine in an operating theatre during heart surgery. This machine takes over the function of the heart and lungs, enabling surgeons to stop the heart while operating. It allows them to take more time to operate and prevents blood from obscuring the operation site. The machine oxygenates the blood and removes carbon dioxide. It also heats the blood to the correct temperature before pumping it back into the patient's body. Heart-lung machines may be used in coronary bypass operations or to repair conditions such as aortic aneurysm.