Regarding the cause of pectus excavatum, there have historically been many hypotheses. For a while, medical experts believed that pectus excavatum was caused by the backward pulling of the diaphragm behind the sternum. Thus, for a time, surgeries abroad involved cutting the portion of the diaphragm behind the depressed area of the chest. Eventually, it was discovered that such cutting did not significantly benefit the treatment of pectus excavatum, and the results were not very conclusive. Therefore, this hypothesis was later debunked. To date, it is generally believed that the primary formation of pectus excavatum is somewhat related to genetic or hereditary factors. Of course, not all cases of pectus excavatum are due to parents having the condition; it might be present in the genes of ancestors and only manifest in the current generation or in this patient. Additionally, pectus excavatum could be associated with other diseases, such as connective tissue disorders. For example, some patients might have congenital diaphragmatic hernias, and after surgical repair, they could be prone to pneumothorax. Furthermore, some patients may suffer from pectus excavatum due to subglottic stenosis and underdeveloped bronchopulmonary structures, possibly triggered by respiratory factors. However, no matter the details, the formation of pectus excavatum is directly or indirectly related to congenital genes or heredity.