Safe cardiopulmonary bypass has been paramount from its first use in the early 1950s until the present. The original perfusion circuits incorporated complex feedback loops and multiple safety devices. As circuits improved and became simpler to operate, advances in safety did not always keep pace. Surveys have illustrated areas that needed improvement and extra attention has been focused on those problems. As the field of perfusion evolved, so has the perfusionist. Perfusion has progressed from on-the-job training to formalized training, certification, and accreditation, and is now approaching national standardization. As the computer age proceeds, the use of safety devices and feedback mechanisms whose developments have been aided by the newly available technologies increases. As the 21st century approaches, cardiopulmonary bypass will continue to become safer, but the perfusionist must continue to stay up-to-date in education and remain vigilant while in the operating room.