Attempts Using Closed Surgery
In May 1948, Gordon Murray, in Toronto, closed an atrial septal defect in a 12-year-old girl by passing two sutures through the atrial septum, tying the sutures and closing the defect (right figure). The surgery was successful but fourteen months later catheterization revealed that the hole was not completely closed. The main drawback of this method was difficulty in placing the sutures, uncertainty in the closure of the defect, and postsurgical emboli.
In January 1952, Charles Baily successfully repaired a large septal defect in a thirty-eight-year-old woman by a method which he called “Atrio-septopexy” (left figure). He made an incision in the right atrial wall, inserted his finger through the hole to investigate the right atrium and the defect, and then sutured the right atrial wall to the rim of the defect. He used this technique in twenty patients total, fourteen of which had the secundum defect; the mortality rate was 14.3% -- an improvement on the alternative methods which had been used during the past 4 years.
In April 1952, Robert Gross and collaborators in Boston developed another technique which they called “Atrial Wall” (right figure). They attached a funnel-shaped rubber “well” to the right wall of the atrium, through the base of which they could insert their finger into the right atrium to easily explore and repair the defect. The well was primarily used to prevent the overflowing of blood. The first three results of this operation were unsuccessful but on April 15, 1952 a nine-year-old boy recovered successfully. He went back to school and could ride his bike comfortably. Catheterization showed complete closure of the defect. Gross used this technique on a number of patients but his method was complicated and other surgeons were not able to repeat it. 
Development of Hypothermia
It was becoming evident that progression in Cardiac Surgery could only be obtained through the development of methods which allowed direct vision and a dry field. Two promising techniques at the time were total cardiac inflow occlusion and hypothermia.
Total cardiac inflow occlusion was used in the laboratory on animals for over 50 years, but it wasn’t until late 1940’s that Richard Varco, at the University of Minnesota, used it on a human. He operated successfully on four patients. In the later years additional operations were done using this method, but the strict time restriction remained an obstacle.
Hypothermia was mainly being used in attempts to treat cancer, schizophrenia, leukemia, and drug addiction. In the late 1940’s W.G. Bigelow, a surgeon at the University of Toronto became interested in Hypothermia to obtain direct vision in intracardiac surgeries. His successful results, on 13 monkeys in 1951, were a promising starting point.
On September 1952 at the University of Minnesota, Richard Varco and John Lewis anaesthetized a patient with ASD, and slowly cooled the patient with refrigeration blankets to 28 degree centigrade. They then opened the chest, occluded the vena cava, opened the right atrium, and closed the ASD. This was the first intracardiac operation performed in a dry operating field under direct vision.
During the early fifties, different methods of induced hypothermia were developed – including bathing the patient in ice water (above figure), using drugs, and cooling the chest cavity with cold saline – but the major drawbacks, arrest of blood flow to the brain and other organs such as the kidneys, was still a problem. 
The first successful open heart surgery
In May 6, 1953, a major breakthrough was achieved when John H. Gibbon (right photo), at the Jefferson Medical College in Pennsylvania, performed the first successful open heart surgery on an eighteen-year-old girl with an atrial septal defect. For this operation he used the Gibbon-IBM heart lung machine, developed over the past decade and a half, with the help of engineers from IBM in New York. Gibbon used the machine on two more patients but neither of the patients survived. The biggest problem was the design of the blood oxygenator resulting in embolism. 
Use of Cross Circulation
During the following years much of the progress was made by C. Walton Lillehei, a surgeon from University of Minnesota, who decided to re-examine the bypass method using simple methods.
In September 1953, Morley Cohen with the aid of his wife Joan and Herbert Warden conceived using a Human as a blood oxygenator. Two tubes would be used; one carrying the oxygenated blood from the donor to the patient and another would return the deoxygenated blood from the patient to the donor (top left photo). The idea was presented to Lillehei.
In April 20, 1954, Lillehei and Varco operated the first successful cross circulation operation on a four-year-old boy, with ventricular septal defect, a much more critical condition where there is a hole in the septum seperating the ventricles. Lillehei and Varco operated on the patient while Cohen and Warden monitored the donor (top left photo). [1,2]
Development of the Bubble Oxygenator
In Summer of 1955, Richard De Wall of University of Minnesota, together with Lillehei (standing at left in photo), developed the first bubble oxygenator. His device was an instant success and was used throughout the world because it was inexpensive, easy to assemble, and heat sterilizable. Throughout the years to come, oxygenator designs became more advanced, eventually leading to the development of membrane oxygenator and hollow fiber oxygenators. Today Atrial Septal defect and more complicated procedures are performed using the heart-lung machine with antraoperative comlication rates of only 1%. [1,2]
Atrial Septal Defect played a crucial role in the development of open heart surgery primarily due to the functionally non-critical location of the defect and the ease and speed of the repair.
Development of Transcatheterization
In 1976 the first successful transcatheter closure of atrial septal defect was reported by T.D. King and N.L. Mills. Throughout the years this non-surgical method of atrial septal defect closure has become a routine procedure. However this method has it’s limitation regarding the size and location of the defect. Today, this method is only used to close secundum atrial septal defects smaller than 25 mm.