The Ross operation is a surgical intervention in which a diseased aortic valve is replaced by the pulmonary valve of the same patient. A donor valve replaces the pulmonary valve. In this thesis, several key unanswered clinical questions are explored. Early mortality after the Ross operation is relatively high in neonates. However, neonates and infants who survive the early post-operative period show impressive improvement of left ventricular function, preservation of autograft valve function and freedom from reoperation. Surgeons nowadays attempt to perform a valve-sparing reoperation in adult patients who require reoperation after the Ross operation for autograft root dilatation and/or valve insufficiency. This approach is associated with low morbidity and mortality. However, a large proportion of patients with isolated autograft valve insufficiency require a reintervention within the first two post-operative years. Histological and biomechanical analysis of explanted autograft valves and vessel wall has led to increased insight into remodelling after the Ross operation. Explanted autograft valves show a phenotype which is distinct from both native pulmonary and aortic valves. The explanted autograft shows a decrease in wall stiffness compared to the native pulmonary artery and aorta.