John H. Gibbon achieved in 1953 the first successful open-heart surgery with a heart-lung machine, correcting an atrial septal defect in an 18-year-old patient under extracorporeal circulation. The machine — developed over more than two decades with IBM's support — maintained circulation and oxygenation outside the body while the heart was stopped. The conceptual and technological barrier had been overcome: the heart had ceased to be inaccessible. Gibbon could not reproduce the success in subsequent cases and withdrew from extracorporeal circulation research, but his 1953 achievement is one of the greatest milestones of 20th-century surgery.