On the other hand when pulmonary stenosis is severe, blood in the right ventricle has to escape through the septal defect during ventricular contraction and a right-to-left shunt results.

另一方面，当肺动脉狭窄严重时，心室收缩过程中，右心室的血液不得不通过室间隔缺损分流，形成右向左分流。