The relationship between adolescent idiopathic scoliosis (AIS) and pectus excavatum (PE) is not well understood. We hypothesize that the combined thoracic malformations of AIS and PE may lead to a “double crush to the thorax” resulting in greater cardiopulmonary impairment than either thoracic malformation in isolation. We evaluated the Haller index (HI) and thoracic volume changes that occur pre- and post-operatively for kyphoscoliosis and PE by examining the case of a 12-year-old girl who had a “double crush to the thorax.” Using posterior-to-anterior and lateral standing scoliosis films obtained before and after both operations we determined the PE severity index (HI). Using the same radiographs a Blender based computational model was used to approximate the thoracic volumes. With correction of kyphoscoliosis the HI acutely increased from 1.9 to 3.2 with a decrease in thoracic volume of 11% resulting in shortness of breath and tachycardia. With PE repair the HI was returned to normal (HI = 2.4) and the thoracic volume increased 18%, with resolution of her cardiopulmonary symptoms. When severe kyphoscoliosis and PE co-exist consideration should be given to the implication of the “the double crush to the thorax” if cardiopulmonary symptoms arise.