Cardiopulmonary bypass in the clinical setting is barely 40 years old. Yet worldwide, it is used in the operating room in more than 500,000 cases a year. This broad acceptance is a tribute to the vision of gifted investigators who could see beyond the mere technical problems of perfused isolated organs. They integrated mechanical concepts, knowledge of materials, and sheer inventiveness with an appreciation of physiological issues to address the clinical needs of open-heart surgery.