Echocardiographic measurements of the left ventricular dimensions and wall thicknesses at end diastole and end systole, aortic root and left atrial dimensions, mitral valve E-F slope, left ventricular ejection fraction, percent fractional shortening of the left ventricular internal dimension, estimated left ventricular mass and percentage systolic thickening of the ventricular septum and left ventricular free wall were obtained in 105 normal subjects ranging from one day to 23 years of age. Each parameter was found to follow a linear regression upon one of three functions of the body surface area. The internal dimensions of left ventricle, the left atrium, and the aortic root, and the mitral valve E-F slope varied in a linear relation to the cube root of the body surface area. Thickness of the ventricular septum and left ventricular free wall varied in a linear relation to the square root of the body surface area. Estimated left ventricular mass varied linearly with the direct measurement of body surface area. Ejection fraction, percent fractional shortening of the left ventricle and percent systolic thickening of the ventricular septum and left ventricular free wall were independent of body surface area despite a marked increase in the size of the left ventricle during normal growth and development.