Position of the heart in the rib cage of an infant, pediatrics. The heart is not centered in the rib cage. But it is shifted to the left. An infant's heart is positioned more horizontally than in a child or adult. So its apex arrives at the level of the 4th left intercostal space. He retains this position until the age of 4. While between 4 and 6 years old, the heart gradually shifts to position the apex at the level of the 5th intercostal space. Therefore, at age 7, the heart is on the same axis as that of an adult.