Understanding the lung mechanics and gas exchange in healthy human lungs might be a step forwards in the way of understanding diseased lungs. One way to do that is by modeling the entire lung including the effect of gravity on distribution of ventilation and perfusion down the lungs. However, gravity has been estimated to cause a minor effect on perfusion distribution. The aim of this study is to use a model of per- fusion designed by Mogensen et al. (2010) to investigate the hypothesis that anatomical differences in the lungs have the major effect on per- fusion distribution down the lungs. To be able to answer this hypothesis, the study has imple- mented two anatomical gradients, namely length and number of capillaries surrounding the alveoli. By adjusting these gradients, the model is cali- brated to fit an experimental data measured by Jones et al. (2001) describing distribution of perfusion in supine position. The hypothesis is then investigated, experimenting the perfusion distribution In silico in prone posture to evaluate the effect of the anatomical difference on distribution heterogeneity in the lungs. The result of the experiment is in agreement with studies suggesting that the distribution pattern of pulmonary perfusion is due anatomical differences in the lungs.