A perfusionist, also known as a clinical perfusionist, is a trained health professional who operates the heart-lung machine during cardiac surgery and other surgeries that require cardiopulmonary bypass. The perfusionist is a highly trained member of the cardiothoracic surgical team which consists of cardiac surgeons, anesthesiologists, physician assistants, surgical technicians and nurses. The perfusionist’s main responsibility is to support the physiological and metabolic needs of the cardiac surgical patient so that the cardiac surgeon may operate on a still, unbeating heart. This is accomplished through the utilization of the heart-lung machine, as well as its associated components of an oxygenator, filters, reservoirs and tubing. The perfusionist is solely responsible for the circulatory and respiratory functions of the heart-lung machine. In addition, there is a spectrum of physiologic parameters that are constantly monitored by the perfusionist that ensures that the circulatory and respiratory needs of the patient are being met and allows the cardiac surgeon to focus on the actual surgical procedure and less on the immediate needs of the patient. Other responsibilities include autologous blood collection and processing, implementation and management of the intra-aortic balloon pump, adult and infant extracorporeal membrane oxygenation (ECMO) as well as monitoring of anticoagulation, electrolyte, acid-base balance and blood-gas composition. In many tertiary hospitals, perfusionists are also key personnel in placing and managing patients on ventricular assist devices as bridge to recovery or heart transplantation and supporting patients receiving lung or liver transplants. In certain hospitals, perfusionists can be involved in procurement of cardiothoracic donor organs for transplantation.