(blā′lŏk″-hăn′lŏn )
[Alfred Blalock, U.S. surgeon, 1899-1965; C. Rollins Hanlon, U.S. surgeon, b. 1915]
The surgical creation of an atrial septal defect or enlargement of the foramen ovale in an infant with transposition of the great arteries. This procedure helps to improve oxygenation until total repair is undertaken.