Heart weight, ventricular wall thicknesses, and valve circumferences were measured in 200 autopsy specimens of normal hearts from persons who ranged from birth to 19 years old. During this period of body growth, all cardiac measurements increased progressively and correlated with both age and body size (height, weight, and surface area). For most measurements, the mean predicted values were greater in male than in female subjects. Heart weight correlated better with body weight and body surface area than with body height or age of patients. In contrast, ventricular wall thicknesses and valve circumferences correlated better with age of the patients than with measurements of body size. In both sexes at all ages, the thickness of the left ventricle was greater than that of the right ventricle and was generally less than that of the ventricular septum. The circumference of the tricuspid valve usually exceeded that of the mitral valve, but aortic and pulmonary valve circumferences were similar. On the basis of these data, equations were derived and reference tables were constructed to predict normal values for heart weight, ventricular wall thicknesses, and valve circumferences.