If you read the textbooks, the natural history of unrepaired cyanotic congenital heart disease is bleak. Truncus arteriosus—or common arterial trunk—one of the more rare cyanotic lesions estimated at 1:10000 live births, is certainly no exception. By 12 months of age, less than 10% of patients with unoperated truncus arteriosus are alive.1
T. H. (who asked that I use her real initials) did not read the textbooks.
Elder RW. Learning From Improbable Longevity. JAMA. 2013;310(19):2041-2042. doi:10.1001/jama.2013.276685