Summary.Roentgenologic determination of the heart volume has been carried out in 45 infants with healthy hearts. The roentgenograms were taken simultaneously in two planes at right angles (the frontal and sagittal planes), and the volume calculated by Jonsell's modification of the Kahlstorf formula. In order to ascertain the error of the method a number of control examinations were made on cadavers, and in addition double determinations were made in 18 infants at the time of the roentgen examination. The absolute values for the heart volume were correlated with the body length and the body‐weight and the heart volume per square metre of body surface with the body lengt