Until the late 1950s, and Senning's operation, the condition was commonly fatal. The defect causes blood from the lungs to flow back to the lungs and blood from the body to flow back to the body.
Until the late 1950s, the condition was often fatal due to its impact on circulation. However, with Senning's operation, the defect could be corrected, allowing for a reversal of blood flow that restored normal circulation.