Modern heart surgery was developed fundamentally in the nineteen-fifties together with the extra-corporeal circulation, based on the use of the heart-and-lung machine, making it possible to replace heart valves and to correct certain congenital heart disorders; this as a whole was designated "open heart surgery", as the heart itself, its ventricles and internal functional parts were opened during the operation.
As a natural extension of this method, the coronary bypass surgery emerged in the mid-sixties, also based on the use of the same per-operative technology, viz. the heart-and-lung machine. In this case the surgeon, although not having to operate within the heart itself, needed peace to work in the operating field, i.e. the "coronary tree", the heart's own circulatory system, substantially embedded in the surface of the heart in the form of two main stems--right and left--gradually branching out down along the heart, finally to end deep below the surface in the form of the end-arterial branches of the heart musculature.
Thus, the techniques already established by the use of the heart-and-lung machine were taken over directly, although the coronary bypass operation could not be categorized as "open heart surgery", but rather as "closed heart surgery"--simply to have peace and quiet in the operating field.
The use of the heart-and-lung machine involves a trauma to the heart itself, and more or less serious complications will often appear post-operatively, during intensive care as well as later; thus, in short, a so-called post-perfusion syndrome has been described.