Heart weights, ventricular wall thicknesses, and valve circumferences were measured in 765 autopsy specimens from normal hearts from persons 20 to 99 years old. Body weight was a better predictor of normal heart weight than was body surface area or height, and mean heart weights were greater in men than in women at all ages. When heart weights were indexed (divided by body surface area), the mean values per decade increased significantly in women between the 3rd and 10th decades of life (P less than 0.01) but remained relatively constant with time in men. We found no significant differences in ventricular wall thicknesses between men and women. Although indexed mean values for left and right ventricular wall thicknesses remained relatively constant in all decades, ventricular septal thickness increased significantly between the 3rd and 10th decades of life (P less than 0.001). Beyond the seventh decade of life, the mean ratio of septal to left ventricular free wall thicknesses exceeded 1.20, and the upper 95% confidence limit exceeded 1.50--an important consideration in evaluation of hypertrophic cardiomyopathy in elderly patients. Mean valve circumferences were usually greater in men than in women, but the opposite pertained when values were indexed by body surface area. In both sexes, all indexed mean valve circumferences increased progressively throughout adult life, although this trend was greater for semilunar than for atrioventricular valves. The mean circumference of the aortic valve surpassed that of the pulmonary valve in the 4th decade and approached that of the mitral valve by the 10th decade of life. Thus, in evaluation of annuloaortic ectasia, investigators should take into account the normal age-related changes in aortic valve dimensions.