IN 1935 Master, Dack and Jaffe1 carried out the first investigation on precordial leads in 72 healthy children. They recorded seven precordial leads each separated by a distance of 2 cm. at the level of the fourth intercostal space, beginning at the left margin of the sternum, and found that the T wave, initially negative, became positive in the proximities of the apex. A year later Rosenblum and Sampson2 recorded in 15 children the chest-back lead and three precordial leads in the second, third and fourth intercostal space at the left margin of the sternum. Contrary to what was shown by their controls (66 records on adults without cardiac lesions in which the T wave was negative), this wave was found to be positive in the precordial leads in 64 per cent of the children, diphasic or iso-electric in 32 per cent and negative in only 4 per