Position of the apex beat in childhood.

The position of the apex beat in relation to the midclavicular and nipples lines and the intercostal spaces was studied in 353 healthy Jamaican children from birth to 10 years. The traditional use of the midclavicular line as a reference point in relation to the apex beat is not an accurate index of normal heart size at all ages. For this purpose actual measurement of the apex beat, which ranges between 2.8 and and 5.4 cm from the midline, should be made. However, for a rough estimate of normal cardiac size the midclavicular line may be used. In contrast, the nipple line lies outside the apex beat at all ages; it should not be used in the clinical evaluation of normal cardiac size. From birth to age 3 years the apex beat is located in the 4th intercostal space and with increasing age gradually moves into the 5th space in most children.