 Before this technique became available, in 1950, two cardiac surgeons, Blalock and Hanlon, had developed a palliative procedure which consisted in opening the atrial septum.Being that in TGA the atrial septum prevents oxygenated blood from reaching the systemic circulation, this simpler procedure leads to improvements in systemic arterial O2 saturation.With the Senning surgical repair, a baffle – or conduit - is created within the atria that reroutes the deoxygenated blood coming from the inferior and superior venae cavae to the mitral valve and therefore to the pulmonary circulation  This is accomplished by creating a systemic venous conduit that channels deoxygenated blood from the superior and inferior vena cava towards the mitral valve.