heart-lung machine, device that maintains the circulation of the blood and the oxygen content of the body when connected with the arteriovenous system; it is also called the pump oxygenator. The machine is used in open-heart surgery when it is necessary to effect a bypass of the circulatory system of the heart and lungs. The oxygenator repeatedly draws off the blood from the veins, reoxygenates it, and pumps it into the arterial system. The contractions of the heart are halted by running a potassium citrate solution through the coronary vessels. The surgeon is thus enabled to open the heart and make the necessary repairs while the heart is still and his view is not obstructed by blood.