The aim of this study was to investigate the possibility of determination of lung changes in congenital deformity of heart and vessels by the method of Weibel and Elias (1967) for count of points in the lung (volume of alveoli and interstitium). The results show that this method is suitable for the estimation of quantitative changes in Morbus Fallot. In order to decide the degree of arteriosclerosis an additional measurement of the wall thickness of lung vessels is necessary in cases of ventricular septal defect. The arteriosclerosis is an important factor for the secondary variations, especially of the right heart. A field of application of this method could be the praeoperative lung biopsy for the clarification of the question of operability.