To determine the growth rate of the human heart in relation to body surface area, normal data obtained by echocardiography and angiocardiography were analyzed with respect to changes in body size occurring between infancy and adulthood. Published data were used to determine the following for 7 theoretical subjects ranging in size from 0.2 m2 (normal newborn) to 2.2 m2 (large adult): average left ventricular (LV) end-diastolic diameter; aortic root diameter; right pulmonary artery diameter; aortic valve area; LV end-diastolic volume; and LV mass. Linear dimensions (LV, aortic and right pulmonary artery diameter) increased as a square root function of surface area and could not be described by a constant "index" of dimension to surface area. Aortic valve area was linearly related to surface area and equalled 3.4 cm2/m2 for subjects of all sizes. LV volume and mass were exponentially related to surface area. This study indicates that intracardiac areas may be indexed for body surface area, but that linear dimensions and volumes have a nonlinear relation to surface area and are more appropriately indexed by surface area to the 0.5 and 1.5 power, respectively.